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The University of Iowa
Center for Credit Programs
Distance Education Study Guide
for
027:053 Human Anatomy
College of Liberal Arts and Sciences Integrative Physiology
Course Prepared by
Kenneth E. Mobily, Ph.D.
3 Semester Hours 8 Written Assignments
4 Examinations
027:053 Human Anatomy
Copyright © 2007 The University of Iowa. All rights reserved.
No part of this publication may be reproduced in any form by any means
without permission in writing from the publisher.
r 1/95 r 4/98 r 3/02 r 7/05 r 7/07
r 12/07
The University of Iowa prohibits discrimination in employment and in its educational programs and activities on the basis of race, national origin, color, creed, religion, sex, age, disability, veteran status, sexual orientation, gender identity, or associational preference. The University also affirms its commitment to providing equal opportunities and equal access to University facilities. For additional information on nondiscrimination policies, contact the Coordinator of Title IX, Section 504, and the ADA in the Office of Equal Opportunity and Diversity, 319.335.0705 (voice) or 319.335.0697 (text), 202 Jessup Hall, The University of Iowa, Iowa City, Iowa 52242-1316.
If you are a person with a disability who requires
reasonable accommodations in order to participate in this program, please contact the Center for Credit Programs to discuss your needs.
Distance Education Division of Continuing Education
250 Continuing Education Facility Iowa City, IA 52242-0907
Telephone: 319.335.2575 • Toll free: 800.272.6430
Fax: 319.335.2740 • E-mail: credit-programs@uiowa.edu Web: http://continuetolearn.uiowa.edu/ccp/
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027:053 Human Anatomy College of Liberal Arts and Sciences
Integrative Physiology
Course Contents
Course Lessons
About the Coursewriter and Instructor ................................................................... 5!Introduction: About This Course ............................................................................. 6!
Overview ........................................................................................................ 6!Course Goals .................................................................................................. 6!Required Course Materials ........................................................................... 7!How To Study ................................................................................................ 7!Web and E-mail ............................................................................................. 9!Examinations ............................................................................................... 11!Evaluation and Course Grade ...................................................................... 11!
UNIT 1 INTRODUCTION ..................................................................................... 13!Lesson 1 Orientation ............................................................................................. 14!Lesson 2 Embryology ............................................................................................ 18!UNIT 2 BASIC ORGANIZATION.......................................................................... 24!Lesson 3 Cells ........................................................................................................ 25!Lesson 4 Tissues .................................................................................................... 31!
Written Assignment #1 ............................................................................... 38!Lesson 5 Integumentary System ........................................................................... 40!Lesson 6 Bone and Skeletal Tissue ....................................................................... 45!
Written Assignment #2 ................................................................................ 51!Examination #1 ............................................................................................ 51!
UNIT 3 MOVEMENT ............................................................................................ 52!Lesson 7 The Axial Skeleton .................................................................................. 53!Lesson 8 The Appendicular Skeleton .................................................................... 59!Lesson 9 Joints ...................................................................................................... 66!
Written Assignment #3 ............................................................................... 70!Lesson 10 Muscle Tissue ........................................................................................ 71!Lesson 11 Muscle System ...................................................................................... 77!
Written Assignment #4 ............................................................................... 83!Examination #2 ........................................................................................... 83!
UNIT 4 INTEGRATION ........................................................................................ 85!Lesson 12 Nervous Tissue ..................................................................................... 86!Lesson 13 Central Nervous System ....................................................................... 94!Lesson 14 Peripheral Nervous System ................................................................ 108!
Written Assignment #5 .............................................................................. 114!Lesson 15 Autonomic Nervous System ................................................................ 116!
Written Assignment #6 .............................................................................. 121!Lesson 16 Special Senses ...................................................................................... 122!
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027:053 Human Anatomy
Lesson 17 Endocrine System ............................................................................... 129!Examination #3 .......................................................................................... 135!
UNIT 5 VISCERAL SYSTEMS............................................................................. 136!Lesson 18 Heart .................................................................................................... 137!Lesson 19 Blood Vessels and Lymphatics ........................................................... 144!
Written Assignment #7 .............................................................................. 154!Lesson 20 Respiratory System ............................................................................. 155!Lesson 21 Digestive System ................................................................................. 162!
Written Assignment #8 ............................................................................. 169!Lesson 22 Urinary System .................................................................................. 170!Lesson 23 Reproductive System .......................................................................... 175!
Examination #4 (FINAL) ............................................................................ 180!Course Evaluation ...................................................................................... 181!Transcript ................................................................................................... 181!
Distance Education Policies and Instructions
Be sure to read the Distance Education (DE) Policies and Procedure before beginning this course. It is available on the ICON course site under Content; students who order the optional print material will receive a print copy by mail.
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About the Coursewriter and Instructor
KENNETH E. MOBILY received his
bachelor's and master's degrees in therapeutic
recreation and was clinical supervisor of
therapeutic recreation in Cincinnati, Ohio, for
three years. He completed his Ph.D. in 1981 from
the University of Iowa in physical education. He is
a Professor at The University of Iowa where he
teaches a variety of professional courses in
therapeutic recreation. He also teaches Human Anatomy for the
Department of Integrative Physiology at Iowa. His primary research area
is exer
obily may be contacted by e-mail at: ken-
cise and aging.
Professor M
mobily@uiowa.edu .
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027:053 Human Anatomy
Introduction: About This Course
Overview
This course is designed to give you a basic understanding of human
anatomy, with particular emphasis on organelles, tissues, organs, and
systems. You will finish this course with a background knowledge of the
structure of the human body. You may want to capitalize on your
introductory knowledge through further study.
In preparing this study guide, I have focused on structure and the
relations between structures. While this may be rather obvious because the
preceding sentence essentially embodies the definition of anatomy, it is
easier said than done.
At the same time, you should be aware that function and structure
are related. How an anatomical component works is almost always related
to its cellular or gross structure. Red blood cells are bi-concave in shape
(structure) and this allows for more surface area for the cell to bind and
transport oxygen or carbon dioxide (function). We have a generous range
of motion (function) at the shoulder joint because of the shape (structure)
of the articulating bones—the head of the humerus and the glenoid fossa of
the scapula. Function often follows form.
Course Goals
Accordingly, the general goals of this course are three:
1. To gain a basic understanding of the organs, systems, and tissues
covered,
2. To relate systems and tissue to one another and understand how they
work together,
3. And to understand the role of each organ, system, and tissue.
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Required Course Materials
Materials Provided by the CCP
The following items may be accessed from the ICON course site
(under “Content”). They are also available in print from our office, and
may be purchased for an additional fee.
! Course Study Guide ! Course Syllabus ! Textbook and Materials Order Form ! Distance Education Policies and Instructions
Textbooks/Course Materials to Purchase Independently
! Marieb, Elaine, Jon Mallatt, and Patricia Wilhelm. Human Anatomy, 5th edition. San Francisco, CA: Pearson-Benjamin Cummings, 2008.
The course textbooks may be ordered from a local bookstore (see
Textbook and Materials Order Form) or from the vendor of your choice.
Note: If you purchase items from an alternate bookseller, it is imperative
that you obtain the correct editions.
How To Study
The units of study are organized around general concepts. These
organizing concepts are indicated below by unit numbers, with course
lessons indicated by letters. The chapters in Marieb, Mallatt, and Wilhelm
pertaining to the lessons are indicated to the side of each.
Unit 1: Introduction
A. Orientation (Chapter 1)
B. Embryology (Chapter 3)
Unit 2: Basic Organization
A. Cells (Chapter 2)
B. Tissues (Chapter 4)
C. Integumentary System (Chapter 5)
D. Bone and Skeletal Tissue (Chapter 6)
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027:053 Human Anatomy
Unit 3: Movement
A. Axial Skeleton (Chapter 7)
B. Appendicular Skeleton (Chapter 8)
C. Joints (Chapter 9)
D. Muscle Tissue (Chapter 10)
E. Muscle System (Chapter 11)
Unit 4: Integration
A. Nervous Tissue (Chapter 12)
B. Central Nervous System (Chapter 13)
C. Peripheral Nervous System (Chapter 14)
D. Autonomic Nervous System (Chapter 15)
E. Special Senses (Chapter 16)
F. Endocrine System (Chapter 25)
Unit 5: Visceral Systems
A. Heart (Chapter 18)
B. Blood Vessels (Chapter 19) and Lymphatics (Chapter 20)
C. Respiratory System (Chapter 21)
D. Digestive System (Chapter 22)
E. Urinary System (Chapter 23)
F. Reproductive System (Chapter 24)
At the beginning of each lesson you will be provided with a list of
objectives. You should use the objectives to guide your reading and
studying. You will find that some lessons have few objectives, while others
have a rather lengthy list.
Hence, you are not responsible for material that does not pertain to
the objectives. However, do not allow this to make you casual about your
reading and studying. First of all, successful completion of the written
assignments requires that you know and apply the objectives. The same
is true of the examinations.
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Translated, this means that you are expected to know the material
and objectives very well. This also means that when I tell you to study a
figure or exhibit, I expect that you will study it and not just glance at it.
Anatomy is a very visual science. Lacking actual specimens, the visual
representations of structures become critical. In fact, I would suggest that
you photocopy those illustrations containing a lot of information and clip
off the labels. Then, use the illustration without labels as a self-test at the
end of a unit to determine the extent of your understanding.
Another study hint pertains to pacing. Do not expect to cram for
examinations one or even two days before. You will find that there is a lot
to know. Therefore, learning a little bit every night is a lot easier than
waiting until the "11th hour." Also, review previously covered material
every few days to keep it "fresh" in your mind. Anatomy does require
discipline, but I believe you will find it pays dividends by the end of the
course.
You will also find several sample multiple-choice questions at the
end of each lesson. There are two purposes to the questions. First, they will
help you anticipate the question format you will find on the examinations.
Secondly, the questions will help you home in on objectives you need to
study more. Answers to the questions can be found at the end of each
lesson.
Web and E-mail
This course is delivered on the World Wide Web via ICON (Iowa
Courses Online) http://icon.uiowa.edu/. You can access the course by
logging into ICON with your Hawk ID and password.
Online Tutorials
http://www.uiowa.edu/~online/tutorials/tutorial.html
View the online tutorials, which are provided in Flash format:
topics include instruction on using ICON, WebMail, Hawk ID Tools,
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Security, and more. Please be aware that Distance Education courses do
not use all of the components explained in the ICON tutorial.
Technical Support for Online Students
Technical assistance, including FAQs, software demos and
downloads, and contact information are provided on our technical support
pages: http://continuetolearn.uiowa.edu/ccp/sos/.
Hawk ID Help
http://hawkid.uiowa.edu/
Your Hawk ID and password are sent to you via email or mail the
first time you register at The University of Iowa. If you have forgotten
your Hawk ID password or it has expired (after six months), you may call
the ITS Help Desk at the University and ask them to reset your password.
Please feel free to call our toll-free number (800.272.6430) and select the
phone routing option that connects you with the ITS Help Desk.
E-mail Alias
http://continuetolearn.uiowa.edu/ccp/sos/email.htm
A University of Iowa e-mail alias was created for you when you
enrolled in this course, if you didn't already have one. Your email alias
forwards messages to a specified email address, which can either be a UI
student email account or a non-UI account (e.g. Hotmail, Yahoo…etc.).
Once created, all subsequent e-mail contact from The University of Iowa
will go to your UI email alias. If you have not done so already, you should
login to your student account, i.e. ISIS http://isis.uiowa.edu/, then go to
My Uiowa/My Email and either request a UI email account or provide a
routing address.
E-mail is an official method of communication at The University of
Iowa; you are responsible for all information sent to your e-mail address of
record, and you may carry on official transactions with the University by
sending e-mail from your e-mail address of record. It is important that you
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keep your email routing address in ISIS current if you prefer to use a non-
UI email account.
Examinations
The examinations are forty questions/forty points. The exams stress
application, understanding, and knowing the objectives. Exams are
multiple choice with four foils (choices) for each question. Each exam is
designed to cover about one fourth of the material. However, because
some lessons contain more objectives than others, the number of lessons
covered on each test differs. The exams are NOT comprehensive.
Material Covered on the Exams
Examination #1 Covers lessons 1–6
Examination #2 Covers lessons 7–11
Examination #3 Covers lessons 12–17
Examination #4 Covers lessons 18–23
Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
Evaluation and Course Grade
The course consists of eight written assignments and four exams. A
total of 240 points are possible: four exams at 40 points each, (160) and
eight assignments at ten points each (80).
8 Written assignments 80 points (10 percent each) 4 Examinations 160 points Total possible 240 points
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027:053 Human Anatomy
Grading Scale
The grading scale for this class is: 90 percent—A, 80 percent—B, 70
percent—C, 60 percent—D, less than 60 percent—F. Final course grades
will not include plus or minus marks.
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UNIT 1 INTRODUCTION
Lesson 1 Orientation
Lesson 2 Embryology
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027:053 Human Anatomy
Lesson 1 Orientation
Reading Assignment
Read Chapter 1 in the text, focusing on the content that pertains to
the objectives listed below.
Objectives
By the end of this lesson, you should be able to:
1. Define the following levels of structural organization: chemical,
cellular, tissue, organ, system, organism (see Figure 1.1). Give
examples of cells, tissues, organs, and systems.
2. Know anatomical terminology: anatomical position, planes
(saggital, frontal, transverse), body cavities (dorsal, ventral,
thoracic, abdominopelvic, mediastinal, cranial, pleural, pericardial,
vertebral, and viscera). See Figures 1.4, 1.5, 1.9, and 1.10.
3. Define regional and directional terms used in association with the
body (see Figure 1.4 and Table 1.1).
4. Understand anatomical and directional terms in relation to one
another.
5. Define mucous membranes and serous membranes. Identify the
following types of serous membranes: visceral and parietal layers of
the pleura, pericardial, and peritoneum (see Figure 1.10).
Discussion
Most people think of anatomy as the study of things you can see
with unaided vision. Although this is particularly true of the present
course, as Figure 1.1 in the text indicates, anatomy can pertain to the study
of structure at a variety of levels—from chemical through organism. We
will emphasize the study of cells, tissues (groups of similar cells that work
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together), organs (made up of two or more tissues) and systems (a
collection of organs with like functions).
Probably the most critical concept to grasp initially is that of the
anatomical position. It is illustrated in Figures 1.3 and 1.4. Note that it
consists of the body in standing position, head erect and forward, feet
shoulder-width apart, arms at sides, and palms forward. The terminology
that you will also learn in this unit is worthless if you do not know the
anatomical position. All of the terms are used in reference to the
anatomical position. Also, learn the regional terminology (1.4).
Next, study the directional terms in Table 1.1. As a self-test, cover
the definitions of terms and look at yourself in a mirror. See if you can
place each regional term on your own body correctly.
Also, try using the terminology to place body parts relative to one
another. For instance, the abdomen is ventral to the vertebral column.
(Note synonyms; I could have said that the abdomen is anterior to the
vertebral column.) Another example: the shoulder is proximal to the hand.
Try some of these out yourself.
Planes are hypothetical sheets that cut the body or anatomical
structures into two parts. As you can see in Figure 1.5, there are three
planes. The frontal plane cuts the body into front and back parts. The
transverse plane cuts the body into top and bottom parts. The saggital
(median) plane cuts the body into right and left parts. Often the parts that
a plane cuts the body into are equal halves, but this is not always true.
Body cavities are spaces that contain structures. The principal body
cavities you have to know are given in Figure 1.9. Note that the ventral
body cavity is further subdivided into thoracic and abdominopelvic.
Likewise, the dorsal body cavity is subdivided into the cranial cavity and
vertebral cavity. In turn, the thoracic cavity contains special spaces that
house the heart and accessory cardiac structures (pericardial cavity in the
mediastinum) and the lungs (two pleural cavities). Any structure found
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027:053 Human Anatomy
within the ventral body cavity is referred to as viscera. Thus, viscera labels
a category of organs which includes the heart, lungs, small intestines,
stomach, and so on.
Now turn to Figure 1.2 and study the placement of systems in the
body cavities. Some vital organs are exclusively located within certain body
cavities. Place the brain, spinal cord, heart, lungs, and digestive system
into body cavities for practice.
Mucous membranes are found lining tubes entering or exiting the
body. Mucous secreted onto these membranes serves a protective function.
For instance, the mucous membranes lining the nasal cavity and upper
respiratory tract trap inspired pollutants and pollens. Mucous membranes
also line the oral cavity and rectum.
Most of the organs in the ventral body cavity are completely or
partially covered by serous membranes. Serous membranes are double
layered and have an outer parietal layer and an inner visceral layer (see
Figure 1.10). The visceral layer actually adheres closely to the organ. The
layers are identified by organ, for example, the heart is surrounded by a
parietal pericardium and an inner visceral pericardium (see Figure 1.10).
The inner visceral layer actually adheres closely to the organ. The
layers are identified by organ; for example, each lung is surrounded by a
parietal plevia and a visceral pleura. A slight space between the two serous
layers contains serous fluid, which acts as a lubricant for the movements
made by organs when they are
active.
Sample Questions
Questions 1-7 require you
to identify planes or directions
indicated on the figure.
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Foils for Questions 1-7:
Distance Education The University of Iowa
a. saggital b. transverse c. frontal d. cranial e. caudal f. lateral g. medial 1. This is the ______ direction.
2. This is the ______ direction.
3. This is the ______ plane.
4. This is the ______ plane.
5. This is the ______ direction.
6. This is the ______ direction.
7. This is the ______ plane.
8. Which of the following is incorrect about anatomical relations to the palm of the hand in the anatomical position? a. The palm is anterior to the dorsal surface of the hand. b. The hand is distal to the shoulder. c. The hand is medial to the abdominopelvic cavity. d. The hand is cranial to the thigh.
9. The lungs are located in this space.
a. dorsal body cavity b. abdominal cavity c. mediastinum d. thoracic cavity
10. What is the opposite of superficial?
a. lateral b. proximal c. internal or deep d. ipsilateral
Answers to Sample Questions
1. d; 2. e; 3. b; 4. c; 5. f; 6. g; 7. a; 8. c; 9. d; 10. c
In this course, you will submit your first assignment following Lesson 4.
Go on to Lesson 2.
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027:053 Human Anatomy
Lesson 2 Embryology
Reading Assignment
Read Chapter 3 in the text. Use the objectives listed below to guide
and focus your reading.
Objectives
1. Define the following: embryonic period, fetal period, blastocyst,
zygote, blastomere, cleavage, morula, amniotic sac, yolk sac, germ
layer, endoderm, ectoderm, mesoderm, notochord, neural crest,
somite.
2. Summarize developmental events during the first week of the
embryo, from fertilization to blastocyst.
3. Describe the formation of the three primary germ layers
(gastrulation) during week three of the embryo. Especially be able
to explain development of the nervous system (neurulation) from
neural plate to neural tube.
4. Summarize anatomical structures and tissues that are derived from
each of the primary germ layers.
5. Define the following common birth defects and their possible
etiologies: heart defects, mental retardation, spina bifida, Down's
syndrome, cleft palate, cystic fibrosis.
Discussion
Fertilization occurs in the distal (lateral) one third of the uterine
(Fallopian) tube of the female (see Figure 3.3). It results from the union of
an egg cell and a sperm cell, creating a new cell called a zygote. Soon after
fertilization occurs, the zygote begins to divide rapidly and form smaller
segments called blastomeres. This process of rapid cell division is referred
to as cleavage. By the time the dividing zygote nears the medial section of
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the uterine tube, it is known as a morula ("mulberry," ball of cells). The
morula is ready to begin the next phase of embryonic life, implantation.
The morula enters the uterus of the female about day four or five
following fertilization. In doing so the morula also begins to change its
internal anatomy (see Figure 3.4). Cells in the center begin to differentiate
(specialize) and form an inner cell mass (see Figure 3.3e). The remaining
space on the inside is represented by a space known as the blastocyst
cavity. The structure that was referred to as a morula when it entered the
uterus is now known as the blastocyst, with an inner cell mass and outside
cells known as the trophoblast.
The trophoblast cells on the outside of the blastocyst are
responsible for implanting the blastocyst into the uterine wall where it
may thrive in a nutrient rich environment until the fetal membranes can
fully develop and supply the growing infant with needed oxygen and
nutrients from the mother. The trophoblast accomplishes this task by
secreting powerful digestive enzymes that help the blastocyst "eat" its way
into the endometrium (inner layer of the uterine wall). As this process of
implantation occurs, note (see Figure 3.4) that the inner cell mass of the
blastocyst is beginning to change.
These changes signal the beginning of the next stage of embryonic
development, gastrulation. Gastrulation means cell movement, although
the process amounts to more than simply the movement of cells. By
around day nine (see Figure 3.4) the inner cell mass is made up of two
layers of cells, the epiblast and the hypoblast. The movement of cells of the
epiblast constitutes the process of gastrulation seen in Figure 3.5.
The beginning of the formation of the primary germ layers is
indicated by the appearance of the primitive streak, a raised groove on the
external surface of the epiblast (see Figures 3.5 and 3.6). The end result of
the process of cell movement will be the creation of a three-layered
embryonic disc in place of the earlier two-layered disc. The new three-
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layered disc will be comprised of the primary germ layers, the cells that
will form all of the structures that will become the infant.
Formation of the primary germ layers occurs when the cells of the
epiblast invaginate at the primitive streak in two successive waves. The
first cells to invaginate or "tuck under" become the endoderm and the
second group of cells invaginate to become the mesoderm. Cells that
remain in the original position of the epiblast cells become the ectoderm.
Figures 3.5 and 3.6 also demonstrate the formation of another
structure about the same time as gastrulation occurs, the notochord. The
notochord can be thought of as a precursor to the adult vertebral column.
But make certain to understand two things at this point:
1. The notochord is not part of the spinal cord, although it does
contribute to the formation of a structure found in the vertebral
column in adult life (the intervertebral disc).
2. The vertebral column is not the same thing as the spinal cord; the
latter is the nervous component housed within the vertebral
column.
However, the appearance of the notochord does correlate with the
development of the nervous system, derived from some of the cells of the
ectoderm. Figure 3.7 illustrates the process of neurulation, the formation
of the nervous system from the overlying ectoderm. Most of the process is
pretty obvious in Figure 3.7. Cells superior to the primitive node (the
swelling at one end of the notochord) differentiate and thicken, producing
a neural plate. The plate then deepens into a groove, which in turn folds
over itself, forming a neural tube. The superior extent of the neural tube
becomes the brain. The remainder develops into the spinal cord.
At the same time the neural tube is developing, cells immediately
lateral to the tube are pulled along with the deepening neural groove and
come to rest just lateral to the neural tube. These cells are referred to as
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the neural crests. They will develop into a number of structures, most
significantly, sensory nerves.
Weeks three and four in the life of the embryo are very busy, and
another important development is happening in conjunction with that of
the nervous system, differentiation of the mesoderm. The same Figure 3.7
that illustrates neurulation also shows movement and differentiation of
the mesoderm cells into three distinct groups. The first is the somites or
paraxial mesoderm. These cells reside close to the central axis of the
embryo near the notochord and the neural tube. Somites will contribute to
the formation of portions of the axial skeleton, the vertebrae and ribs, the
dermal layer of the skin, and much of the muscle system.
The intermediate section of the mesoderm forms some of the
organs in the ventral body cavity (e.g., kidneys, testicles, ovaries). The
most lateral portion of the mesoderm forms the cardiovascular system,
outer components of the digestive system, parietal membranes, and bones
and ligaments of the extremities.
In mentioning the adult structures that develop from the mesoderm
alone, the student might conclude that trying to keep straight which
structures develop from which of the three primary germ layers is a
daunting task. But there is an easier way to master the task than pure rote
memory. The trick when trying to remember any classification scheme
with two or more categories is to try to remember the easier categories
first. This means the number of categories to remember will be one less
than the total number. In the present case, there are three categories to
remember: ectoderm, mesoderm, and endoderm. I am suggesting that you
need only remember two of the three, as follows.
The ectoderm forms the outer layer of the skin (epidermis), the
nervous system, some bones of the skull and some glands. The endoderm
forms the inner walls of the digestive and respiratory systems, the lower
portion of the urinary system, and some glands. Everything else is formed
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027:053 Human Anatomy
from the mesoderm. So by process of elimination, you know what is
formed from the mesoderm without having to remember its derivatives in
a rote manner. Refer to Figure 3.10 for details of the structures formed
from each germ layer.
Hence, by the end of the embryonic period (0-2 months) almost all
of the necessary structures for survival are in place. The remainder of the
gestation is referred to as the fetal period. It consists primarily of growth
and maturation of structures put in place during the embryonic period.
Moreover, most serious birth defects (congenital defects) appear in the
embryonic period. It stands to reason that the problem will be more
serious if it develops earlier, since all subsequent structures are formed
from the three layers of the embryonic disc and its subsequent folding and
cell movement. In other words, the earlier a problem develops, the more
tissues that are affected, because the problem is perpetuated or passed
along into all structures formed from the affected structure.
Several examples of the more frequent birth defects are discussed in
the "A Closer Look" box at the end of the chapter. Although I will only
discuss one of those defects below, you should have a sense of which
embryonic structures are affected relative to each of the defects listed on
your objectives. Notice how many of the birth defects listed could be
avoided by living a healthy lifestyle and not abusing substances. Maternal
health is therefore crucial to the normal development of the infant.
Spina bifida in its most severe form is a neural tube defect. It results
from a failure of the distal/caudal end of the neural tube to close. The child
is born with a lesion called a "cele," most often found in the lower lumbar
or sacral areas. The resulting deficit is typically paralysis of both lower
extremities and incontinence. The child born with spina bifida may have a
problem with the cranial end of the neural tube as well and often presents
with a condition called hydrocephalus, "water on the brain." This problem
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as well as the paralysis resulting from spina bifida can be managed with
early detection and intervention.
Sample Questions
1. The morula forms as a result of this process. a. gastrulation b. neurulation c. implantation d. cleavage
2. Cells that eventually form the three primary germ layers are derived from this structure. a. trophoblast b. blastocoel c. embryonic disc d. notochord
3. Blood vessels form from this embryonic germ layer. a. ectoderm b. mesoderm c. endoderm
4. This term refers to cell movement. a. cleavage b. gastrulation c. neurulation d. implantation
5. Stem cells are derived from this structure in the embryo (you will have to research this one by reviewing the chapter closely). a. Inner cell mass b. trophoblast c. morula d. yolk sac
Answers to Sample Questions
1. d; 2. c; 3. b; 4. b; 5. a
Go on to Lesson 3.
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UNIT 2 BASIC ORGANIZATION
Lesson 3 Cells
Lesson 4 Tissues
Written Assignment #1
Lesson 5 Integumentary System
Lesson 6 Bone and Skeletal Tissue Written Assignment #2
Examination #1
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Lesson 3 Cells
Reading Assignment
Read Chapter 2 in the text, focusing on material that pertains to
objectives listed below.
Objectives
By the end of this lesson, you should be able to:
1. Identify the structural components of a prototypical cell in an
illustration: plasma membrane, mitochondrion, endoplasmic
reticulum, golgi apparatus, nucleus, lysosome, centriole, ribosome,
and cytoplasm. See Figure 2.1.
2. List the functions of the cellular components in #1 above. Refer to
Figures 2.2, 2.5, 2.7, 2.8, 2.9, 2.10, 2.12, 2.13, 2.14, 2.15, 2.17, 2.18.
3. Identify the role of organelles involved in a secretion pathway
illustrated in Figure 2.8.
4. Generally, define the structure and function of a chromosome
(DNA).
5. Define mitosis, dysplasia, hyperplasia, hypertrophy, and necrosis.
Discussion
In the seventeenth century, Robert Hooke, an English physician,
was the first scientist to use the term "cells." Only later did scientists come
to fully appreciate the importance of Hooke's discovery. The cell is the
basic functional unit of the body. Like any of the larger functional units we
will study, it has a structure—it is an assembly of various parts.
The most basic of these parts is the cell or plasma membrane. The
cell membrane "marks off" the cell as an entity unto itself. It is essentially
a two-layered arrangement of phospholipids and proteins (see Figure 2.2).
This two-layered enclosure controls the entrance and exit of materials into
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and out of the cell proper. You should try to get a sense of the factors that
affect the permeability of the cell membrane (e.g., size of molecule). The
cell membrane can have special places on its outer surface, called receptor
sites, to interact with certain chemicals, such as neurotransmitters and
hormones.
Within the confines of the cell membrane, we find the remaining
parts of the cell: the structures called organelles and the fluid between the
structures, called cytoplasm. Cytoplasm is largely water, making it an
excellent medium for chemical reactions.
Starting with the nucleus, then, we will continue to study the
structure and function of the other parts of the prototypical cell. You
should continuously refer back to Figure 2.1 for study of the shapes of
organelles so that you can identify them later. Notice that small
illustrations for most organelles are found throughout the chapter.
The nucleus (Figure 2.13) is the "brain" of the cell. It almost
completely determines what the cell will do. It has its own membrane,
similar in structure to the general cell membrane. Within the nucleus we
find the genetic material of life, DNA (see Figure 2.14). It appears as
chromatin or chromosomes depending on whether the cell is actively
mitotic or not. DNA, RNA, and proteins are found in the nucleolus, a small
rounded body within the nucleus proper. (We will have more to learn
about DNA later.)
Ribosomes are sometimes called the "anvils" of the cell because
they are the sites where proteins are "forged" (assembled). Amino acids,
the building blocks of proteins, are brought to the ribosome for assembly
into a protein. Ribosomes can be attached or free. Attached ribosomes
appear as small dots (see Figure 2.6 for ribosomes attached to
endoplasmic reticulum) adhering to another structure, the endoplasmic
reticulum. Free ribosomes are just that—free-appearing in the cytoplasm
as unattached dots.
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Endoplasmic reticulum (Figure 2.5) appears as adjacent walls that
form channels, usually found close to the nucleus. If the endoplasmic
reticulum has ribosomes attached, it is called rough or granular
endoplasmic reticulum. If it does not have ribosomes attached, it is
referred to as a smooth or agranular endoplasmic reticulum. Endoplasmic
reticulum is sometimes specialized according to tissue type. For instance,
endoplasmic reticulum in muscle cells is specialized to facilitate
contraction and therefore given a special name—sarcoplasmic reticulum.
(The sarcomere is the functional unit in a muscle cell). The most
important functions of endoplasmic reticulum are storage and
transportation of various materials, but it also helps mechanically support
the cell because of its relatively substantial presence within the cytoplasm.
The golgi apparatus (Figures 2.7 and 2.8) is thought to work with
the endoplasmic reticulum and ribosomes to complete a network
responsible for a product, generally a protein, destined for secretion from
the cell. For instance, after the ribosome produces a product, the
endoplasmic reticulum transports it to the golgi apparatus. The golgi
apparatus then "packages" the product in a way that allows it to pass
through the cell membrane more easily. The golgi apparatus appears as a
stack of "pancakes" with globules floating away from it. The latter are
called secretory vesicles. Secretory vesicles might contain an enzyme to
help digest food, if the cell is in the stomach, or a different product if the
cell is located elsewhere in the body.
The nucleus, endoplasmic reticulum with ribosomes, and the golgi
apparatus, are linked together in cells that actively produce and secrete
useful products (e.g., digestive enzymes). Study Figure 2.8 to see how
these organelles work together in a secretion pathway.
The mitochondrion is often referred to as the "powerhouse" of the
cell because it is responsible for synthesizing energy for the cell's use in the
form of ATP. (ATP molecules can be thought of as batteries.) As can be
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observed in Figure 2.10, the mitochondrion looks like an oblong capsule or
coated tablet on the outside. But on the inside, viewed in the cut-away
portion of Figure 2.9, the mitochondrion has many convolutions or
"shelves" known as cristae. These shelves are produced when the inner
membrane of the mitochondrion folds onto itself. This folding
exponentially increases the surface area for reactions, and hence, energy
formation. (By the way, such folding is a good example of how function is
facilitated by structure.) Because of their involvement in energy formation,
you might logically suppose that very active cells would contain many
mitochondria. This is precisely the case. For instance, muscle cells contain
many mitochondria.
Lysosomes are round structures with fairly thick membranes to
hold their contents—powerful enzymes with the potential to destroy the
cell itself. They are also produced by the golgi apparatus. Lysosomes are
not smooth spheres; rather, their surface is irregular and uneven. Because
of their contents, lysosomes are sometimes called the "suicide packets" of
the cell. More often, however, in the healthy cell, the lysosome can destroy
unwanted invaders that pose a danger to the integrity of the cell or ingest
other "worn out" cellular organelles. For instance, white blood cells
(leukocytes) contain many lysosomes.
Centrioles are long, narrow cylinders located within a greater
structure called a centrosome (see Figure 2.12). Centrioles arrange
themselves in a very organized fashion, appearing as nine evenly spaced
bundles of microtubules. Viewed from the side (Figure 2.12c), the
microtubules of the centriole look like spokes in a wheel. Centrioles are
active in the process of mitosis (cell duplication). They seem to assist in
the movements of chromosomes during mitosis.
DNA is frequently studied in its highly organized state, in the form
of a chromosome, a state it assumes just prior to and during cell division.
DNA looks like a ladder that has been twisted. This is often called a double
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helix arrangement of DNA. The vertical portions of the ladder are
composed of repeating sequences of sugars and phosphates (Figure 2.14).
The horizontal parts of the ladder, where one might place a foot, are made
up of two nitrogen bases. There are four different bases (see "C," "G," "A,"
and "T" in Figure 2.14) in all and the ways in which these bases are
matched up form a sort of code or blueprint for the formation of proteins
and RNA. This is accomplished by portions of the DNA molecule
unraveling and fresh bases being matched up or paired with those
exposed. Accordingly, specific lengths of the DNA molecule correspond to
specific proteins or types of RNA. Lastly, when the entire DNA molecule
unravels, it can completely replicate itself. This happens just before
duplication of the entire cell during the process of mitosis.
Mitosis (Figure 2.18) is the type of cell division that results in two
new/daughter cells that are identical to the parent cell—each has the exact
same 23 pairs of chromosomes. Mitosis is necessary for growth and
development early in life, and for maintenance of tissues the remainder of
life.
Interphase is basically the time in a cell's life between mitotic
divisions (see Figure 2.17). Mitosis consists of four phases that result in the
formation of two daughter cells genetically identical to the parent cell.
Interphase and mitosis are summarized in Figure 2.17.
During interphase the cell is preparing for cell division as well as
carrying on its normal functions. The cell grows and synthesizes an
identical set of DNA for use in the subsequent division. As you can see in
Figure 2.17, interphase takes quite a long time compared to all four of the
phases that make up mitosis.
You do not need to know the details of mitotic division. You should
be able to define mitosis and explain its importance for growth and
maintenance.
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Look up definitions of terms listed in the final objective at the end
of the chapter. Also, look over the "A Closer Look" window at the end of
the chapter, which discusses cancer, and read the short section on aging.
Sample Questions
Try to answer the questions below after you have read Chapter 2,
satisfied the objectives, and studied the figures indicated. Use the
questions as a self-test. If you miss some of the questions, go back to the
chapter to study the material again and find out why you missed the
question.
1. Name the organelle associated with packaging and secreting materials from the cell. a. golgi apparatus b. mitochondrion c. lysosome d. nucleus
2. Where would you expect to find the most ATP? a. in the cell membrane b. in the DNA molecule c. in the mitochondrion d. in the chromosomes
3. Name the structure whose spherical, external surface is irregular; it contains enzymes strong enough to destroy the entire cell. a. centriole b. nucleus c. golgi complex d. lysosome
Answers to Sample Questions
1. a; 2. c; 3. d
Go on to lesson 4.
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Lesson 4 Tissues
Reading Assignment
Read Chapter 4 and pages 125-126 in your textbook with emphasis
on the topics covered by the objectives below.
Objectives
By the end of this lesson, you should be able to:
1. Define a tissue and describe four basic tissue types.
2. Identify the functions of epithelium. Contrast the general
characteristic of epithelium with the general characteristics of
connective tissue: proportion of matrix, proportion of cells, vascular
supply, basement membrane, embryonic derivative, location.
3. Briefly list the structure and function of simple, stratified, pseudo-
stratified, transitional and glandular epithelium (Figure 4.3).
4. Identify the four types of adult connective tissue (CT proper,
cartilage, bone, blood) and describe the following structures found
in loose (aveolar) connective tissue (Figure 4.11): fibrocytes,
collagen fibers, elastic fibers, reticular fibers, and ground substance
or matrix.
5. Compare and contrast the different types of connective tissue:
connective tissue proper, cartilage, bone, and blood (see Figures
4.9, 4.12).
6. Describe the inflammatory response and repair process; identify the
four classic symptoms of the inflammatory response.
Discussion
A tissue is a group of similar cells that work together to accomplish
a common purpose. We will spend considerable time later in this course
studying two of the four basic tissue types—muscle and nervous tissue.
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The remaining types of tissue are epithelial and connective. Histology is
the study of structure and function of tissues. For now, you should get a
general sense of how to discriminate between the four tissue types. Most
people have difficulty discriminating epithelial and connective tissues, so
we will spend most of the time in this lesson focusing on those two tissue
types.
Basically, epithelial tissue does two things. It covers things
(covering/lining epithelium) or it forms glands. Regardless of the type,
epithelium has some definite characteristics you can use to distinguish it
from connective tissue. These include: tightly packed cells, little
intercellular substance (called matrix), a basement membrane (that
supports epithelium), derived from all three layers of the embryo
(ectoderm, mesoderm, endoderm) and no direct blood supply (avascular)
(see Figures 4.1–4.2).
Covering or lining epithelial tissue can be further sub-divided on
the basis of the number of layers of cells and whether or not all of the cells
reach the surface or not (see Figure 4.3). Simple epithelium means there is
a single layer of cells (classified by shapes: squamous, cuboidal,
columnar), whereas stratified epithelium has several layers of variously
shaped cells. The former are found in areas where there is little wear and
where materials have to move into and out of channels easily (like the
lining of capillaries of the vascular system). The latter, stratified-type of
epithelium is found in areas that experience considerable wear and tear
(skin, bladder, and some parts of the digestive tract). A specialized type of
stratified epithelium is known as transitional. It is specialized to distend
(stretch). The third general type of epithelium is called pseudostratified
(pseudo means "false") epithelium (see Figure 4.3d). This is because the
cell arrangement looks like it has several layers, but in reality there is only
one layer of cells. The pseudostratified appearance is attributable to the
fact that not all of the cells reach the lumen of the channel they line.
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The second term that is used to label an epithelial tissue (e.g.,
squamous) refers to the cell shape. The various types of epithelium are
illustrated in Figure 4.3. But you are only expected to know the
significance of simple, stratified, or glandular epithelium; you do not have
to know cell shape.
Glandular epithelium comprises both types of glands, exocrine and
endocrine. For now, you simply need to know that endocrine glands
always secrete hormones; exocrine glands never secrete hormones
(although their products are useful). We will discuss glands in more detail
in the lesson on the endocrine system.
Connective tissue can be discriminated from epithelium on the
basis of its rich vascular supply (with the exception of adult cartilage and
ligament), widely separated cells, and substantial intercellular substance
(matrix). Connective tissue is derived exclusively from the mesoderm of
the embryo. Connective tissue does not cover or line, rather it occurs
beneath the surface, deep to covering or lining epithelium. However, the
connective tissue category probably represents a rather surprising
collection of structures that are seemingly unrelated. Bone, cartilage,
tendons, ligaments, and blood are all categorized as connective tissue.
However, they all share in common the characteristics of connective tissue
with respect to vascular supply, cell to intercellular matrix relationship,
embryonic derivative, and location (see Figure 4.9).
For now, we will look at loose (areolar) connective tissue as the
prototypical connective tissue and see what it is made of. Fundamentally,
the remaining sub-types of connective tissue are differentiated on the basis
of fiber types and amounts, cell types, and consistency of matrix. The
matrix of loose connective tissue is composed of a viscous ground
substance. In its normal state, ground substance facilitates the movement
of materials through connective tissue.
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The matrix also includes fibers, mostly collagenous, with some
elastic. As suggested earlier, the amount and type of fiber helps determine
the type of connective tissue. For example, if there is a large amount of the
collagenous fiber type, with very little fluid between, the connective tissue
is likely a tendon or ligament. Collagen fibers are very tough and resist
stretching. Elastic fibers are tough and can be stretched (hence the title
"elastic"). Finally, reticular fibers are often associated with soft organs
(like the liver) where they provide a framework or structure for the organ.
The typical cell of loose connective tissue is the fibroblast/fibrocyte
(see Figures 4.9 and 4.11 and Table 4.2). Authorities believe that fibrocytes
are responsible for production of many of the fibers of loose connective
tissue and the ground substance of the matrix.
Several other cells (macrophages, plasma cells, mast cells, various
white blood cells) can be found in loose connective tissue. Their primary
responsibility is defense of the body against disease and infection. The
placement of these cells that comprise part of the body's immune response
makes sense since they serve to form a second line of defense if a "germ"
finds access to the body through a cut that penetrates the epidermis.
Loose connective tissue is only one of several types of connective
tissue proper. The others are dense regular, dense irregular, elastic,
reticular, and adipose. Each is specialized according to the amount and
types of fibers found in the matrix.
Dense connective tissue is dominated by collagen fibers (Figure
4.12). If the collagen fibers line up in parallel rows, then it is dense regular
connective tissue. This type of connective tissue is characteristic of
ligaments and tendons, where a lot of strength is needed in one direction.
If the fibers run in various directions, then it is dense irregular connective
tissue. This is characteristic of the dermis layer of the skin (covered in the
next lesson) the periosteum of bone, and the capsules surrounding
synovial joints.
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Reticular connective tissue (Figure 4.12) is understandably
dominated by reticular fibers. Reticular fibers are capable of forming a
framework or "scaffold" for other tissues to attach to. This is why reticular
connective tissue characteristically forms the structural part (stroma) of
many soft organs, such as the liver, spleen, and lymph nodes.
Elastic connective tissue (Figure 4.12) can be found in large arteries
near the heart that experience a lot of stretching when blood is forcefully
ejected into them from the right or left ventricle. Elastic connective tissue
can also be found in ligmentum flavum between the lamina of two
vertebrae where considerable stretching occurs. As you might have
deduced, elastic connective tissue is distinguished from others by virtue of
its generous compliment of elastic fibers.
Adipose tissue (see Figure 4.12) is made up of fat cells (adipocytes)
and is designed for storage of fat droplets within the cytoplasm of the fat
cells.
Mature cartilage distinguishes itself from connective tissue proper
in several ways. First, unlike most connective tissue, cartilage does not
receive a good vascular supply. Second, the typical cell found in cartilage is
a chondrocyte and not a fibrocyte as in connective tissue proper. Finally,
the matrix of cartilage is semi-solid and less fluid than that of loose
connective tissue.
Cartilage comes in three varieties (see Figures 4.12 and 6.1). First
and most plentiful is hyaline cartilage. Hyaline cartilage makes up the
embryonic skeleton, the costal cartilages running from the ribs to the
sternum, and it covers the articular surfaces of bones as they enter into
joints.
Fibrocartilage is considerably less plentiful. It is found between
vertebrae as the outer ring of intervertebral disks, between the two pubic
bones of the bony pelvis as the symphysis pubis, and within some joints as
articular discs (e.g., menisci of the knee).
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The last type of cartilage is elastic cartilage. It is found in only a few
places as well. Elastic cartilage comprises the epiglottis that covers the
trachea as you swallow so that food does not find its way into your trachea
("windpipe"). It also makes up the auditory (eustachian) tube and the
external ear. Hence, you can distort and bend the external ear and it will
return to its original shape.
Bone (see Figure 4.12) is also a type of connective tissue that we will
discuss in another lesson. Like all other connective tissue, it has only a few
cells (osteocytes) scattered in a matrix with collagen fibers. Everyday
observation confirms that a major difference between bone and other
types of connective tissue is that the matrix of bone is solid. This is
because of the deposition of minerals between the osteocytes.
Likewise, blood is also considered connective tissue because it
shares the same features. It has a few cells, erythrocytes and leukocytes,
scattered among a large amount of intercellular matrix called plasma.
Figure 4.9 summarizes the development of all of the types of
connective tissue from the embryonic mesenchyme (mesoderm).
The remaining two tissue types are muscle (Figure 4.14) and nerve
(Figure 4.15). Muscle is specialized to shorten (contract), whereas nervous
tissue is specialized to conduct nerve impulses from place to place. Muscle
and nervous tissue are important enough to warrant in-depth coverage
later in this course.
For now, muscle tissue is found in three types. Skeletal muscle
moves the skeleton. Cardiac muscle is found in the middle wall of the
heart. Smooth muscle comprises the muscular layer of the walls of various
tube-systems (viscera), such as the vascular system.
Nerve tissue is divided into the central nervous system (brain,
spinal cord) and peripheral nervous system (peripheral nerves). It is
specialized to transport "information" we know as a nerve impulse.
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Sample Questions
Make sure you have read the material thoroughly and satisfied the
objectives at the beginning of this lesson before attempting the sample
questions. Try the questions without the aid of book or notes. If you miss a
question, go back and try to determine why you missed it.
1. Which of the following is not a type of epithelial tissue? a. simple epithelium b. cartilage c. stratified epithelium d. exocrine gland
2. Which cell is typically found in loose connective tissue? a. chondroblast b. fibroblast c. osteoblast d. mesenchymal
3. Which statement best describes epithelium? a. It is always arranged as a single layer of cells. b. It contains a large amount of matrix. c. It has an abundant blood supply. d. It has a free border.
4. Tearing a ligament would mean you have sustained damage to this type of tissue. a. epithelial tissue b. connective tissue c. muscle tissue d. nervous tissue
5. A group of cells operating together to perform a specialized activity is called by this name. a. organ b. system c. organism d. tissue
Answers to Sample Questions
1. b; 2. b; 3. d; 4. b; 5. d
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Written Assignment #1
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
Organs are defined as structures that are made up of more than one
tissue. This means that tissues in organs work cooperatively with one
another to accomplish necessary tasks. This assignment is intended to
help you appreciate the cooperative relationships among tissues within
organs, specifically the skin and muscles (both are organs and systems).
Answer all three of the questions below for this assignment.
1. Any given skeletal (voluntary) muscle qualifies as an organ.
Therefore, a cross section through a muscle such as the biceps
brachii would reveal two or more tissue types. In fact, all four of the
basic tissue types are represented in the biceps brachii. Explain,
specifically, where each of the four tissue types is found within the
biceps brachii. (Hint—remember the muscle will have blood supply,
nerve supply, and a means to attach to a bone to produce
movement).
2. Skin (the integument) affords the student an excellent opportunity
to study how epithelial tissue and connective tissue work in
cooperation. One of the major functions of the skin is protection.
Explain how the epithelial portion of the skin (epidermis) and the
connective tissue part of the skin (dermis) serve to protect the
individual.
3. Epithelial cells are the frequent origins of several types of cancer
(e.g., skin cancer, lung cancer, …). Explain why this is the case.
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Identify and explain the attribute of epithelial tissue that is
associated with cancer and how this very same attribute is
beneficial to humans as they age.
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Lesson 5 Integumentary System
Reading Assignment
Read Chapter 5 in the text, paying special attention to answering
the objectives specified below.
Objectives
By the end of this lesson, you should be able to:
1. Define and describe the skin as an organ, and the integumentary
system.
2. Know the functions of the integument.
3. Identify cells typically found in the epidermis, including:
keratinocytes, melanocytes, Langerhans cells, Merkel cells.
4. Identify the layers of the integument and the types of tissues,
structures, and cells found in each layer: epidermis, dermis,
hypodermis/subcutaneous.
5. Define keratin.
6. Describe the following clinical applications: burns (first, second,
third degree, rule of nines), skin cancer.
Discussion
The skin is the largest organ in the body, comprising about seven
percent of a person's total body weight. Including its accessory structures
(hair, nails, …), the skin is also considered a system, the integumentary
system. A system is nothing more than a group of organs working in
common to perform specific functions. However, we will focus on the skin
as an organ within the integumentary system. (Recall that an organ is a
group of tissues that work together to perform common functions.)
The skin as an organ serves a very important protective function for
the body. Mechanical protection is afforded by the outer layer of the skin,
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which is composed of stratified epithelium. Melanocytes in the epidermis
darken the skin upon excessive exposure to UV radiation (sunlight) to
protect deeper structures (blood vessels, red blood cells) from damage.
Finally, cells responsible for defending the body (e.g., white blood cells)
are found in the dermis of the skin to protect against invading germs.
The skin also helps greatly with the regulation of temperature and
receives important sensory information through several general sensory
receptors (e.g., touch, temperature, pressure, pain). Although these are the
primary functions of the integument, you should take note of the
remaining functions: preventing excessive loss of fluid, storage, excretion,
and synthesis of Vitamin D.
As it turns out, the skin is comprised primarily of two tissues we
just studied (in Lesson 4) in some detail. The outer layer of the skin is
comprised of epithelial tissue and called the epidermis, while the middle
layer is connective tissue called the dermis.
The epidermis of the skin is stratified, as you might have expected,
because the skin is a "covering" that experiences considerable wear and
tear. Figures 5.1 shows the epidermis in more detail. As can be seen, it is
comprised of four layers of epithelial cells (Figure 5.3).
Starting with the deepest layer of epidermis we find stratum basale.
Cells of the basale are capable of mitotic division and, hence, serve to
replenish more superficial cells of the epidermis as they are shed via the
wear and tear process.
The stratum spinosum overlies the basale and together with basale
are collectively labeled the stratum germinativum. Spinosum is also
involved in the production of replacement cells for more superficial layers
of the epidermis.
Stratum granulosum represents the first layer of epidermis where
cells are no longer duplicating. Granulosum is active in producing a
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protective "waterproofing" substance for the skin called keratin. Hence,
the outer layer of skin is sometimes referred to as keratinized epithelium.
Stratum lucidum (not shown in Figures) is found only on hairless
surfaces, such as the palmar aspect of the hand. Like granulosum, lucidum
is also involved in keratin production.
The outermost layer of the epidermis is the stratum corneum.
Corneum consists of many rows of dead cells that are progressively
sloughed as they move to the surface. Corneum's many layers are crucial to
satisfying the protective function of skin, even though the cells are dead.
The typical cell of the epidermis is a keratinocyte; it comprises the
multiple layers of epithelium that constitute the epidermis. Melanocytes
are also found in the epidermis. Melanocytes secrete melanin, which
contributes to the pigmentation of our skin. The dark melanin pigment
affords protection for deeper structures against excessive exposure to
ultra-violet radiation from the sun. A third type of cell found in the
epidermis serves a protective function by way of its phagocytic property; it
is called a Langerhans cell. Finally, Merkel cells are thought to serve as
sensory receptors for touch.
The second layer of the skin is known as the dermis (Figure 5.1).
The dermis is considered connective tissue, characterized by a good
vascular supply, more matrix, and fewer cells. Like the epidermis more
superficially, the dermis is layered. Unlike the epidermis, however, it has
only two layers—the papillary and reticular layers.
The papillary layer of the dermis is directly deep to the stratum
basale of the epidermis and sends finger-like projections up into the
epidermis at somewhat regular intervals. These projections are called
dermal papillae. Sometimes the papillae contain sensory receptors for
touch or pressure and capillary loops to bring blood close to the epidermis
(see Figure 5.1). Loose connective tissue is characteristic of this region.
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The reticular layer of the dermis is far thicker and more extensive
than the papillary. This layer contains many glands, like sweat glands, and
nerves running to sensory receptors and to the smooth muscle structures
in the skin. Dense irregular connective tissue is typical of this part of the
dermis.
The final layer is the hypodermis. It contains adipocytes (fat cells)
and loose connective tissue. The hypodermis is the location where excess
fat is frequently stored.
You should skim the remaining portions of the chapter, taking note
of the blood supply to the skin, epidermal derivatives (hair, nails, etc.) and
the different types of exocrine glands found in the skin (sweat and oil
glands primarily). You might find the section on the effects of aging on the
skin and the effects of excessive sun on the skin particularly interesting.
Burns are thermal trauma to one or more layers of the skin (see
Figure 5.11). Burns are graded according to the depth of the skin damaged.
First degree burns affect only the epidermis. Second degree burns damage
the epidermis and part of the dermis. The most serious third degree burn
damages the entire depth of the skin. The most serious acute problem for
the burn victim is excess fluid loss which may lead to life threatening
shock. Until the skin has repaired itself, the long-term problem is risk of
infection. The "rule of nines" is used to determine the extent of trauma
associated with burns. Consult Figure 5.11 to determine how to apply the
rule of nines.
Read the section at the end of Chapter 5 that pertains to cancer.
Sample Questions
1. How many different layers were defined within the epidermis? a. 1 b. 3 c. 5 d. 7
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2. Which of the following types of epithelium is characteristic of the skin?
a. simple b. stratified c. collagenous d. pseudostratified
3. Regeneration of the epidermis is largely the function of which of the
following stratum? a. corneum b. lucidum c. granulosum d. germinativum
4. Which of the following is the deepest layer of the epidermis?
a. papillary b. corneum c. reticular d. basale
5. Merkel cells are found in this layer of the skin.
a. epidermis b. dermis (papillary region) c. dermis (reticular region) d. hypodermis (subcutaneous layer)
Answers to Sample Questions
1. c; 2. b; 3. d; 4. d; 5. a
Go on to Lesson 6.
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Lesson 6 Bone and Skeletal Tissue
Reading Assignment
Read Chapter 6 in your textbook. Again, take special note of those
sections most pertinent to answering the objectives listed below. You will
notice the objectives from this lesson on will generally be more numerous
and detailed.
Objectives
By the end of this lesson, you should be able to:
1. Describe the components and functions of the skeletal system.
2. Identify and give examples of each of the four shapes of bones (see
Figure 6.2).
3. Diagram a long bone; identify each part and describe its functions
(see Figure 6.3).
4. Describe a cross-section through the diaphysis of a long bone,
noting periosteum, compact bone and components of an osteon,
endosteum and medullary cavity (see Figure 6.6). Contrast compact
bone with spongy bone.
5. Describe the process of endochondral ossification (Figure 6.10).
Contrast endochondral ossification with intramembranous
ossification.
6. Briefly explain how bones grow in length and the role the
epiphyseal plate plays in this process.
7. Generally describe remodeling of bone and the role of osteoclasts in
the process.
8. Describe the process of fracture repair.
9. Define and list risk factors for osteoporosis.
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Discussion
Common sense tells us bone tissue protects and supports. But some
of bone's other functions are rather surprising. For instance, bone is a
major reservoir for minerals. This means that the body might sacrifice a
share of bone tissue in order to maintain adequate levels of some minerals,
such as calcium. In fact, the presence of acceptable levels of blood calcium
is absolutely necessary for life. Bone is also involved in blood cell
production (hemopoiesis). Of course, bones also give muscles something
to hang onto, and as a consequence, act as levers to produce movement.
As we noted earlier, bone is one type of connective tissue. It is well
supplied with blood vessels, has few cells (osteoblasts, osteocytes,
osteoclasts) and a great deal of matrix in between the cells. The difference
between bone and other types of connective tissue is that the matrix is
hardened via the deposition of minerals, a process called calcification. Like
most other connective tissues, bone has fibers (collagenous) too.
Identify the four basic bone shapes in Figure 6.2: long, short, flat,
and irregular. Long bones are commonly found in the extremities. Flat and
irregular bones tend to be found in the axial skeleton.
At this point you should turn to Figure 6.3, showing a prototypical
long bone. You need to be able to draw a long bone and label the parts, just
as you see them in Figure 6.3.
After you are able to visually recognize the parts of a long bone, turn
your attention to the function of each part. First of all, the diaphysis and
epiphysis essentially have no function other than being names we use to
identify certain regions on the surface of a long bone. However, the
remaining structures you identified in Figure 6.3 are of considerable
functional significance. Hence, you should learn the functions of these
structures well.
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As you may have surmised from our work with the prototypical long
bone, bone tissue proper takes two basic forms—compact and spongy. In
turn, each of these types of bone has its own unique organization. In
compact bone, the basic structural unit is called an osteon; in spongy bone,
the basic structural unit is the trabecula.
In Figure 6.6, an osteon of compact bone can be seen as it is
organized around a blood vessel. The osteon reminds some people of the
growth rings that can be seen in the trunk of a felled tree. The calcified
matrix appears as a series of layers (concentric lamellae). Between each of
the layers you can see little spaces called lacunae. Inside each lacuna is a
mature bone cell (osteocyte). Finally, notice the small processes radiating
out from each of the lacunae; these are called canaliculi. The canaliculi are
actually channels that are necessary for essential nutrients and oxygen to
reach the osteocytes that are isolated in the lacunae.
Spongy bone can be seen at the epiphyseal ends of long bones and
the endosteum that lines the medullary cavity (see Figure 6.3) and in the
center of flat bones, such as those of the skull (see Figure 6.4). Spongy
bone is much more porous than compact bone and does not organize into
osteons. The structural unit of spongy bone is called a trabecula
(trabeculae is plural). The trabecula takes quite a different form than
compact bone; it is organized into an open lattice-work type of
arrangement. The blood supply is more direct, as blood circulates rather
freely throughout endosteum bone. Thus, you will not find canaliculi in the
trabeculae of spongy bone.
Bone formation (ossification) can take two different routes.
Intramembranous ossification is the more direct of the two, wherein bone
is formed directly from a fibrous membrane (Figure 6.9). More commonly
though, bone (especially long bones) is formed from cartilage. Do not
make the mistake of thinking the former process results in spongy bone
and the latter in compact bone. No structural difference results from the
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two distinct ossification processes. That is, both result in spongy bone and
compact bone.
For the most part, only bones of the skull are formed through
intramembranous ossification. The majority of bones are formed through
the second type of ossification that begins with a cartilage model of the
future bone. This process is called endochondral (within cartilage)
ossification and is diagrammed in Figure 6.10. After the cartilage model is
laid down in the embryo, some cells in the perichondrium become
osteoblasts. At the same time the cells and matrix in the center of the
diaphysis of the cartilage model breaks down, leaving large cavities
(known as cavitation of the model). Next, a periosteal bud penetrates the
diaphysis of the model delivering bone cells secreting osteoid in the center
of the diaphysis. This is the primary ossification center. The future
medullary cavity develops when osteoclasts break down some of the bone
tissue in the center of the diaphysis to create a space.
Next, secondary ossification centers appear at each epiphyseal end
of the bone. The process leading to the formation of the primary
ossification center in the diaphysis is repeated in each epiphysis.
The problem is how to accommodate growth in length and width of
the bone until the individual reaches adulthood. As it turns out, cartilage
persists in the epiphyseal growth plate, located between epiphysis and
diaphysis. (The growth plates have five zones of cartilage; see Figure 6.11.)
The cartilage cells here continue to be actively mitotic and continue to
produce matrix. The cartilage cells and matrix on the epiphyseal side of
each growth plate divide, pushing some cells toward the diaphysis.
Eventually, these cells are calcified, then break down. The remnants of
calcified matrix project into the medullary center of the diaphysis.
Osteoblasts from the diaphysis then adhere to these calcified "stalagtites"
and deposit bone tissue on the remains. Hence, cartilage cells are laying
down matrix on the epiphyseal side of each growth plate while bone is
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eventually replacing cartilage on the diaphyseal side of each growth plate.
This is the way bones increase in length.
Eventually, the process ceases when all the cartilage in the growth
plate is replaced by bone tissue. At this point the epiphyseal plates are said
to be "closed" and the person reaches final adult stature.
Remodeling is accomplished by new bone tissue being laid down on
the periosteal (outer) surface of the diaphysis and being destroyed
(resorbed) on the endosteum (inside) side of the diaphysis. Osteoclasts are
the cells responsible for resorbing bone tissue closest to the medullary
center. As a matter of fact, this process (called remodeling) continues
throughout life and assures that as bone is worn out it will be constantly
replaced. Osteoblasts and osteoclasts that are found in both the
periosteum and endosteum also remodel the bone surfaces.
The process of fracture repair is summarized in Figure 6.14. It
consists of three basic steps: formation of the fracture hematoma (blood
clot), callus formation (cartilagenous and bone), "bridges" over the two
fractured ends. Finally, the fractured area is remodeled and the original
bone is restored.
Osteoporosis is loss of the mineral content in bone tissue in excess
of what might be expected as a result of the normal aging process. The
problem is—why is bone tissue lost? Is it because osteoblasts become less
active; because osteoclasts become more active; or something else? (You
can dig out the answer to this one yourself.) Moderate exercise is thought
to retard the loss of mineral content in bone tissue because it places
optimal stress on bones. The body, in turn, accommodates to stressors and
this may explain why regular exercise tends to be associated with
preserved mineral content in bone. (And you thought exercise was only
good for your muscles and cardiovascular system!)
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Sample Questions
Test yourself with the following questions after you feel comfortable
with the material in Lesson 6. Make sure you check out the questions you
miss.
1. A fracture in the shaft of a bone would be a break in this part of a long bone. a. epiphysis b. periosteum c. diaphysis d. articular cartilage
2. The growth of a long bone in length occurs in this location.
a. epiphyseal plate b. articular cartilage c. periosteum d. center of the shaft
3. Remodeling of a bone is a function of these two cells.
a. chondrocytes and osteocytes b. osteoblasts and osteocytes c. osteoblasts and osteoclasts d. chondroblasts and osteoclasts
4. Name the bone that belongs to the axial skeleton.
a. clavicle b. scapula c. pelvis d. sacrum
5. Identify a bone from those below formed by intramembranous
ossification. a. humerus b. femur c. tibia d. mandible
Answers to Sample Questions
1. c; 2. a; 3. c; 4. d; 5. d
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Written Assignment #2
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Discuss the similarities and differences between loose connective
tissue, dense (regular and irregular) connective tissue, and bone.
2. Define the parts of a long bone and list the functions of each part.
3. Describe the major events of endochondral ossification (use Figure
6.10 to help organize your answer). Begin with formation of the
cartilage model in the embryo.
Examination #1
Examination #1 follows written assignment #2. This will be a one-
hour, supervised examination, covering material in Lessons 1 through 6.
No books, notes, or other aids may be brought to the exam. The
examination consists of forty multiple-choice questions of the same type
you have seen in the sections of sample questions in each lesson, according
to the number of objectives per topic.
Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
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UNIT 3 MOVEMENT
Lesson 7 The Axial Skeleton
Lesson 8 The Appendicular Skeleton
Lesson 9 Joints
Written Assignment #3
Lesson 10 Muscle Tissue
Lesson 11 Muscle System
Written Assignment #4
Examination #2
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Lesson 7 The Axial Skeleton
Reading Assignment
Read Chapter 7 in the textbook. As before, use the objectives to
guide your reading.
Objectives
By the end of this lesson, you should be able to:
1. Categorize bones into either axial or appendicular skeleton (Figure
7.1)
2. Identify the 22 bones of the skull (8 cranial and 14 facial) and
selected landmarks—mastoid process, styloid process, occipital
condyles, foramen magnum, sella turica, cribiform plate, crista galli
(Figures 7.2, 7.3, and 7.4).
3. Locate and identify the hyoid bone (Figure 7.12).
4. Describe the structure of a typical vertebra (Figure 7.15). Identify
the unique features of cervical, thoracic, lumbar, and sacral
vertebrae (Figures 7.16–7.18)
5. Identify the normal curvatures of the spine (Figure 7.13). Which are
primary and which are secondary?
6. Identify and describe the sternum (3 parts) and ribs (true, false,
floating). Explain how the ribs articulate with the sternum and the
vertebral column. (Figures 7.19–7.20)
7. Identify bones and landmarks that form the following joints: typical
intervertebral joint, atlanto-occipital joint, atlanto-axial joint, joints
between rib and vertebra, ribs and sternum, sacrum and ilium.
8. Describe the following impairments: kyphosis, lordosis, scoliosis
and herniated disc (Figure 7.14).
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Discussion
Study Figure 7.1 and be able to classify bones into either the axial or
appendicular skeleton. Bones of the axial skeleton lie along the mid-line or
central "axis" of the body, whereas bones of the appendicular skeleton are
associated with the upper and lower extremities.
The tough part of this lesson and the one that follows will be
disciplining yourself to study the diagrams and learn the bones and
markings listed in the objectives above. The best first step is to review the
bones of the appendicular skeleton versus the bones of the axial skeleton
in Figure 7.1. You will probably want to use this figure quite often to test
yourself. (Remember, anatomy is very visual, so you will have to spend a
lot of time on the illustrations.)
Next, identify the bones of the skull and the landmarks listed in
objective number 1 (Figures 7.2, 7.3, 7.4). The toughest one to picture is
the ethmoid in Figures 7.3 and 7.7. It is a plate of bone pretty much in the
saggital plane, situated directly posterior to the nasal bones. This makes it
difficult to see on almost any superficial view of the skull, though you can
see the superior part of it in the view of the cranial floor in Figure 7.4c (it is
labeled the cribiform plate).
The vertebral column consists of thirty-three individual vertebrae:
seven cervical, twelve thoracic, five lumbar, five sacral (fused) and four
coccygeal (also fused). There are also four normal curves in the vertebral
column throughout its length (see Figure 7.13). Thoracic and sacral curves
are primary (present at birth) and anteriorly concave (curved part
forward), while cervical and lumbar curves are secondary (develop after
birth) and anteriorly convex. Take note of the fact that all normal vertebral
curves are in the saggital plane. No curves are observed on an anterior
view of a normal adult vertebral column.
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Next, study the vertebra in Figure 7.15. Be able to identify all the
parts in a superior view indicated in your objectives. Also note that when
two vertebrae are set one on top of the other a foramen is formed between
two adjacent pedicles. This is called the intervertebral foramen and it is
the route of exit for spinal nerves from the spinal cord. As you can see in
Figure 7.13, when vertebrae are stacked one atop another, they form joints.
These so-called intervertebral joints are slightly movable and allow for
subtle posture adjustments.
You will notice that at each level, the vertebrae take on some very
specialized shapes to do their jobs better. Figures 7.16 through 7.17 will
visually reinforce the differences and similarities between cervical,
thoracic and lumbar vertebrae. Table 7.2 summarizes the important
differences between vertebrae.
The cervical vertebrae are probably the most distinct. C1 (atlas)
vertebra, for instance, is simply a ring of bone with two very large superior
articular facets to receive the occipital condyles (thus forming the
atlanto-occipital joint). The C2 vertebra, or axis as it is sometimes
called, has a distinctive superiorly directed process called the dens. The
dens as well as the superior articular facets of C2 articulate with C1 to form
the atlanto-axial joint. The vertebra prominens, or C7, is palpable if you
reach around behind yourself, flex your head forward and feel at the base
of your neck. That posteriorly directed protrusion is the prominent
spinous process of C7. The remainder of the cervical vertebrae are
characterized by bifid (forked) spinous processes and transverse foramina
(for the vertebral artery).
The distinctive features of thoracic vertebrae relate to the joints
formed with the ribs and the direction of their spinous processes. Thoracic
vertebrae are the only vertebrae with impressions (facets or demifacets)
left by the ribs because they are the only vertebra that articulate with
the ribs. Facets or demifacets are found on both the bodies and
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transverse processes of all thoracic vertebrae. Also, their spinous processes
tend to be very "pointy" and directed more inferiorly than those of cervical
or lumbar vertebrae.
Lumbar vertebrae carry most of the weight of the upper torso and
hence are very "heavy" and "chunky" in appearance. Their spinous
processes point directly posterior and are quadralateral or squared off in
shape. Their superior and inferior articular facets are oriented in the
saggital plane unlike those of the cervical (oriented mostly in the
horizontal plane) and thoracic (oriented in the coronal plane) regions.
The orientation of these articular facets and the intervertebral joints
they form with one another largely determine what kinds of movements
are possible at each vertebral level—primarily rotation of the head in the
cervical region, primarily lateral flexion in thoracic region, and primarily
flexion and extension in the saggital plane in the lumbar area. Study the
orientation of the articular facets at cervical, thoracic and lumbar levels of
the vertebral column.
Between each vertebra is an intervertebral disc (see Figure 7.14).
The discs act as shock absorbers between each vertebra and are exposed to
considerable stress, especially in the lumbar region. The disc is composed
of an outer fibrous ring called the annulus fibrous and a soft inner core—
the nucleus pulposus. Sometimes the nucleus pulposus herniates or
ruptures through a weakened portion of the annulus fibrosus. Pain is
usually present and chronic because of the pressure exerted on one or
more spinal nerves. This condition is known as a herniated disc.
The sternum, sometimes called the "breast bone," has three distinct
parts (see Figure 7.19): the manubrium, body and xiphoid process. Note
the jugular notch which you can palpate on your own body where both
your collar bones converge. You can also palpate the costal margin formed
by the costal cartilages of ribs eight–nine. The costal margins of each side
converge medially at the xiphoid process as the costal angle.
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Also pay attention to the number of ribs that articulate with the
sternum. The upper seven ribs that articulate with the sternum via a costal
cartilage are called "true ribs." You should discern why the remaining five
ribs are called "false ribs."
Figure 7.20 displays a typical rib. Take note of the head, tubercle,
and angle of the rib. In life, intercostal nerves, arteries, and veins run in
between the ribs, protected by the costal groove.
Briefly study Figure 7.20 that shows the joint formed between a rib
and a vertebrae. Figure 7.20 shows an especially good view of the
articulation between the vertebral body and transverse process and
the head and tubercle of the rib.
Posture abnormalities can be exaggerations of normal curves or
curves in a plane other that the saggital plane. Kyphosis is an exaggeration
of the thoracic curve, whereas lordosis is an exaggeration of the lumbar
curve. Both, however, present as curves in the saggital plane. In contrast,
scoliosis is a curve in the coronal plane. Hence, it is much more difficult to
correct.
Sample Questions
1. The dens is found on which of the following bones? a. sternum b. rib c. C2 vertebra d. sacrum
2. This condition is an abnormal curvature of the spine in the frontal
plane. a. kyphosis b. scoliosis c. spina bifida d. lordosis
3. Name the bone directly posterior to the nasal bone.
a. ethmoid b. temporal
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c. occipital d. sphenoid
4. Ribs attached directly to the sternum by means of costal cartilage are
referred to by this name. a. floating b. deviated c. false d. true
5. Which of the following bones is paired?
a. frontal b. mandible c. sphenoid d. zygomatic
Answers to Sample Questions
1. c; 2. b; 3. a; 4. d; 5. d
Go on to Lesson 8.
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Lesson 8 The Appendicular Skeleton
Reading Assignment
Read Chapter 8 in your textbook. As with the chapter on the axial
skeleton, pay close attention to the objectives as you read. Really study the
figures and test yourself on identifying bones and landmarks on the bones.
Pay special attention to the articular surfaces on the bones of the
appendicular skeleton.
Objectives
By the end of this lesson, you should be able to:
1. Identify the bones of the shoulder girdle and important landmarks
on the scapula and clavicle (Figures 8.1–8.2)
2. Identify the bones of the upper extremity (including the hand) and
important landmarks (Figures 8.3–8.5; 8.7).
3. Identify bones and landmarks associated with the following joints:
sterno-clavicular, acromio-clavicular, gleno-humeral, elbow
(including proximal radio-ulnar), wrist, metacarpo-phalangeal,
interphalangeal.
4. Identify three bones that comprise the pelvis and key landmarks
(Figure 8.8).
5. Identify bones of the lower extremity (including the foot) and key
landmarks (Figures 8.10–8.12).
6. Identify bones and landmarks associated with the following joints:
hip, knee (hinge and plane), ankle, metatarso-phalangeal.
7. Describe these clinical applications: fractured clavicle, carpal tunnel
syndrome, metatarsal stress syndrome.
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Discussion
As you can see from the list of objectives, this is another one of
those chapters that requires sustained effort and rehearsal. It makes
considerable sense to approach the bones and markings you have to learn
in logical units. It is very important to learn the bones and their markings
well because many of them are involved in the formation of joints, which
you will study later, and/or serve as points of attachment for muscles,
which you will also learn later. Of course, I continue to recommend that
you photocopy your diagrams, clip off the labels and then try to label the
markings yourself.
I recommend that you begin by studying Figures 8.1, 8.2, 8.3, 8.4,
8.5, and 8.7. This may seem like a lot to begin with, but I do not expect you
to learn the entire shoulder girdle and upper extremity the first time
through. I do believe that you will be surprised by how much you do know
after a couple of rehearsals.
One particularly confusing series of terms includes the conoid
tubercle (on the inferior surface of the clavicle), the coracoid process (on
the scapula) and the coronoid fossa (on the anterior, inferior surface of the
humerus). As you can see, the words are very similar in appearance. But, if
you place the markings in alphabetical order and start with the most
medial and superior bone, then work out and down, you will associate
each marking with the right bone: clavicle-conoid tubercule, scapula-
coracoid process, humerus-coronoid fossa.
Another part of the upper extremity that tends to give people
trouble is the wrist. I have no magic solutions for you, but I do have a
couple of tips. First, learn the bones in two rows of four each—a proximal
row and a distal row. Second, learn the bones in the anatomical position,
anterior or palmer side. Third, remember the bones from the thumb side
in because the thumb (pollex) is the prominent digit of the hand (note that
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metacarpals are numbered 1–5, beginning with the metacarpal associated
with the thumb). Also, do not make the common error of thinking that the
scaphoid bone is the carpal bone proximal to the first metacarpal; as you
can see in Figure 8.7, it is not.
As you study the bones and landmarks of the shoulder girdle and
upper extremity, you should begin to appreciate how the landmarks on
different bones fit together to form the joints that you will study in the
next lesson. The shoulder girdle actually is comprised of three separate
joints between the sternum, clavicle, scapula, and humerus.
The clavicular notch of the manubrium receives the sternal
extremity of the clavicle to form the sterno-clavicular joint. The acromion
of the scapula articulates with the acromial extremity of the clavicle to
form the acromio-clavicular joint (see Figure 8.1a). The glenoid cavity of
the scapula and the head of the humerus form the gleno-humeral joint (see
Figure 8.1a). The latter is the joint that people commonly refer to as the
"shoulder joint," but as you can see, the shoulder is really more than the
gleno-humeral joint alone.
When an individual sustains a "separated shoulder," he has
damaged the acromio-clavicular joint. This is different than a "dislocated
shoulder," which refers to a dis-articulation between the head of the
humerus and the glenoid cavity of the scapula.
Likewise, the elbow joint is comprised of more than one joint. The
articulation between the capitulum of the humerus and the head of the
radius, and the articulation between the trochlea of the humerus and the
trochlear notch of the ulna collectively form the joint we normally call the
elbow joint (see Figure 8.5). But there is another articulation at the elbow
that allows for pronation and supination The articulation between the
head of the radius and the radial notch of the ulna (see Figure 8.5) is
known as the proximal radio-ulnar joint.
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Distally, the radius forms the wrist joint with two of the carpal
bones of the proximal row—the scaphoid and the lunate. Notice that the
ulna is not involved in the formation of the wrist joint.
Finally, joints are formed between the distal end of the metacarpals
(head) and the bases of the associated proximal phalanges—the
metacarpal-phalangeal joints. Interphalangeal joints are formed between
adjacent phalanges (heads articulate with bases). Collectively, the joints of
the hand provide for fine motor movements and allow the human species
considerable precision in the manipulation of tools, appliances, and even
sport devices (e.g., baseballs).
Take the same approach to learning the bones of the pelvic girdle
and lower extremity. Start by rehearsing the bones and markings in
Figures 8.8, 8.10, 8.11, and 8.12 a few times. Then, test yourself over the
material. Again, I believe you will be astounded at the amount of
information you have learned after only a time or two through the
information.
In the pelvic girdle, you have quite a challenge. The pelvic girdle
(Figure 8.8) is composed of three distinct bones that fuse in the
acetabulum. The ilium, ischium, and pubis each contribute about one-
third to the acetabulum. The ilium is the superior bone; the ischium is the
posterio-inferior bone; and the pubis is the anterior-inferior bone. I think
the key to learning the markings on all three bones is keeping yourself
oriented; knowing whether you are looking at the medial or lateral surface
of the pelvic girdle. It seems logical to pick out one key landmark to orient
yourself with. Before I tell you mine, why don't you pick one that makes
sense to you? So long as you are comfortable with the landmark you
picked, there is no reason to adopt mine. But if you like, you are certainly
welcome to use mine—maybe you picked the same one anyway. I like to
use the acetabulum because if I can see it I know I am looking at the lateral
surface of the pelvic girdle. If not, then I must be viewing the medial
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surface. It makes a lot of sense to use the acetabulum to me because I
know the head of the femur must fit into a laterally placed socket in order
to work properly.
Actually, I think you will find the lower extremity a little easier;
there are somewhat fewer bones and fewer markings than with the upper
extremity.
Notice that there are several parallels between the ankle (tarsals)
and the wrist (carpals), and between the phalanges of the hand and the
foot. But don't get over-confident; there is one less tarsal than carpal, and
the metatarsals are numbered from medial to lateral (starting with the big
toe—the hallux), just the opposite of the metacarpals. (This is because the
numbering always begins on the side of the great digit. The thumb is
lateral in the anatomical position, while the great toe is medial in the
anatomical position.)
Again, take breaks in learning the material by answering the health
and clinical application objectives.
As you did while studying the bones of the upper extremity and
shoulder girdle, so too you should take note of the landmarks on bones
that enter into articulations. The pelvic girdle is simpler than the shoulder
insofar as the three bones of the pelvis are fused in the acetabulum and the
only other bone involved is the femur.
The three bones of the pelvis (Figure 8.8); the ilium, ischium, and
pubis, fuse to form the acetabulum. In turn, the acetabulum receives the
head of the femur (Figure 8.10) to form the hip joint. Curiously, a
fractured hip that often results from a fall, especially in older adults, is not
a fracture to the bony pelvis at all. Actually, the neck of the femur is most
often fractured as a result of the trauma associated with the fall, or as a
result of osteoporosis or, more likely, a combination of the two.
The knee joint is formed from three bones (Figure 8.10 and 8.11):
the condyles of the femur, the condyles of the tibia, and the facets on the
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posterior surface of the patella. The flexion and extension at the knee are
accomplished as a result of the articulations between femoral and tibial
condyles. The patella slides superiorly and inferiorly on the femoral
condyles as the knee is flexed and extended (a plane joint). The patella acts
as a pulley for the quadriceps femoris muscle group that produces
extension of the leg (as in kicking a football). The movement of the patella
constantly adjusts the angle of the pull of the quadraceps femoris to
maximize its power. Note that the fibula is not part of the knee joint.
However, the lateral malleolus (Figure 8.11) of the fibula helps form
the ankle joint along with the medial malleolus of the tibia (Figure 8.11)
and the talus (Figure 8.12) of the tarsals. The distal ends of the tibia and
the fibula are held together with a strong ligament to provide stability
between the two bones during weight-bearing and ambulation.
Finally, joints between the metatarsals and proximal phalanges
(Figure 8.12) and between adjacent phalanges are identical to those of the
hand. Hence, the joint of the foot confer considerable mobility to
movements of the toes, even though most of us do not appreciate this
capability.
Note the clinical applications for a fractured clavicle, carpal tunnel
syndrome, and metatarsal stress syndrome. Each clinical application is
explained by short sections distributed throughout Chapter 8.
Sample Questions
1. How many phalanges, carpals, and metacarpals are there in one hand? a. 31 b. 27 c. 22 d. 19
2. A hip fracture is actually a break in this bone.
a. ilium b. ischium c. pubis
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d. fermur
3. On which bone are the glenoid cavity and the acromion found? a. humerus b. tibia c. clavicle d. scapula
4. Name the medial bone of the leg.
a. tibia b. fibula c. calcaneous d. navicular
5. What is the name given to the distal articular surface on the femur?
a. condyle b. intertrochanteric crest c. linea aspera d. favea capitis
Answers to Sample Questions
1. b; 2. d; 3. d; 4. a; 5. a
Go on to Lesson 9.
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Lesson 9 Joints
Reading Assignment
Read Chapter 9 in your textbook. Work through the reading
materials slowly, again paying considerable attention to the figures.
Objectives
By the end of this lesson, you should be able to:
1. Define an articulation and identify factors that limit movement at a
joint.
2. Classify joints by structure and function (Table 9.1 and Figures 9.1–
9.3).
3. Recognize characteristic synovial joint features and frequent
accessory structures: (Figure 9.3).
4. Identify movements possible at synovial joints (Table 9.3, 9.4 and
Figures 9.5, 9.6).
5. Identify the six classes/shapes of synovial joints (Figure 9.7).
6. Compare movements permitted according to the various subtypes
of synovial joints (see assignment at the end of this lesson).
7. Identify skeletal components, movements, joint shapes, ligaments,
and cartilagenous structures at the following selected joints:
Shoulder (gleno-humeral) (Figure 9.8), Elbow (Figure 9.9), Hip
(Figure 9.11), Knee (Figure 9.12), Ankle (Figure 9.15).
8. Define the following clinical applications: sprains, dislocations,
subluxations, arthritis (rheumatoid, osteo, gouty), Lyme disease,
and ankylosing spondylitis.
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Discussion
There is some preliminary work to do that pertains to the first few
objectives; then you can start to study specific joints. To begin with, a joint
is a location where one bone meets another bone or cartilage.
Joints are classified in two ways: by function and by structure.
Functional classification of joints is based on the amount of movement
allowed: immovable (synarthrodial), slightly movable (amphiarthrodial),
and freely movable (diarthrodial).
The structural classification of joints basically looks at how the joint
is held together. If the joint is bound by fibrous connective tissue
(remember the strength of collagen fibers), then it is a fibrous joint
(suture, syndesnosis).
Cartilaginous joints are bound together by (you guessed it!)
cartilage. There are two types of cartilagenous joints. We have actually
considered a synchondrosis already—technically, the epiphyseal plate is
considered a synchondrosis type joint. Costal cartilages also qualify the
articulations between ribs and sternum as a syndhondrosis. Intervertebral
discs qualify as a symphyseal type of cartilaginous joint, the connective
tissue is fibrocartilage.
The more interesting joints for the purposes of sport, exercise, and
human movement are the freely movable joints. This category exclusively
includes synovial joints.
You should study and know the prototypical synovial joint (Figure
9.3) very well. Pay particular attention to the minimal features necessary
for a joint to be classified as a synovial type: joint cavity, articular capsule,
and articular cartilage. As you will find out later, there are additional
structures that you might find in a synovial joint (articular discs,
ligaments, etc.), but those listed above are the minimum number of
structures for a joint to qualify for the synovial category. Synovial joints
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get their name from the synovial membrane that lines the inside of the
joint capsule and secretes the lubricating synovial fluid.
You should next study the types of movements possible at a
synovial joint. I would recommend you use Figures 9.5 and 9.6 and
practice each of the movements. Next, have a friend, spouse, or child test
you by doing each of the movements. Your task would be then to recognize
each of the movements demonstrated.
While you are practicing each of the movements, you might want to
think about those anatomical features that limit movement. There are four
factors that limit movement: muscle strength, tension of ligaments, bone
morphology (shape), and soft tissues. For instance, the shape (structure)
of the trochlear notch of the ulna and the trochlea of the humerus allow for
only one type of angular movement—flexion/extension.
Note some clarifications for movements. In the hand, taking the
fingers away from the mid-line of the hand is abduction; the opposite is
adduction. Technically, circumduction is only possible at ball and socket
joints.
Next, study the different subtypes of synovial joints based on the
shapes of articulating bones. As you can see in Figure 9.7, the shapes
(structure) of articulating bones largely determine the kind of
movement(s) allowed at a synovial joint. Also, once you believe you have
learned synovial joint types fairly well, try to determine the kinds of
movements allowed at each. We will reinforce the relationship between the
structure (shape) of synovial joints and movements possible through the
written assignment at the end of this lesson.
Now for the tough part. Work your way through each of the joints
listed in your objectives and study the figures (9.8 through 9.15) that
pertain to each. Try to get a general sense of how the ligaments are placed.
Identify other accessory structures (articular discs, etc.). For example, you
should know that collateral ligaments prevent abduction and adduction in
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the coronal/frontal plane at hinge joints. Hence, collateral ligaments
stabilize joints such as the elbow and the knee.
Don't overlook the articulating bones, the type of joint you are
studying, and the movements possible at each joint listed in the objectives.
Make sure to study the material in Table 9.2 that pertains to each joint.
Take breaks by reading the clinical applications identified in Objective 8.
Remember, do not try to learn everything in one or two nights. Also
remember to test yourself using the copy machine and label method
employed in earlier lessons.
Sample Questions
1. What is the name given to a joint that is united by a dense ligament of fibrous connective tissue? a. gliding joint b. synovial joint c. cartlaginous joint d. fibrous joint
2. What is the clinical term applied to excessive stretching or tearing of
ligaments? a. dislocation b. strain c. sprain d. bursitis
3. This is the special name given to extension of the foot at the ankle joint.
a. hyperextension b. plantar flexion c. dorsiflexion d. abduction
4. Which of the following is not a synovial joint?
a. plane b. hinge c. symphysis d. ball and socket
5. Which ligament below is found at the elbow joint?
a. radial collateral
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b. zona orbicularis c. transverse acetabular d. posterior cruciate
Answers to Sample Questions
1. d; 2. c; 3. b; 4. c; 5. a
Written Assignment #3
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Compare and contrast knee and elbow joints, noting similarities
and differences between the two. Think about structural and
functional joint type, placement and number of ligaments, number
of bones and articulations in each joint, and movements possible at
each joint.
2. The gleno-humeral joint and the hip joint both qualify as ball and
socket joints. Explain why the gleno-humeral joint seems to be
more mobile then the hip even though both joints are ball and
socket. Explain why the gleno-humeral joint is injured more
frequently.
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Lesson 10 Muscle Tissue
Reading Assignment
Read Chapter 10 and pages 540-542; 649-651 in your textbook. It is
important to really follow your objectives closely because some aspects of
muscle function are not your responsibility. Of course, I still recommend
that you read everything, but spend more time studying the objectives.
Objectives
By the end of this lesson, you should be able to:
1. Describe the major characteristics and functions of muscle tissue.
Identify the parts of a muscle (origin, belly, insertion).
2. Define and contrast the three different types of muscle (skeletal,
cardiac, smooth). See Table 10.2.
3. Identify and describe the different connective tissue components in
muscle (Figure 10.1).
4. Define the basic components of a skeletal muscle cell (fiber). (See
Figures 10.4 and 10.6.) Draw a sarcomere. Briefly explain muscle
contraction at the level of the sarcomere (see Figures 10.4 and
10.8).
5. Identify the components of a neuromuscular junction (see Figure
10.9). Define a motor unit and its implications for precise
movements versus gross body movements.
6. Discuss the concept of muscle tone and its implications for posture.
7. Define these clinical applications: muscular dystrophy, muscle
strains, atrophy, hypertrophy, fibromyalgia, and a muscle cramp.
Summarize the detrimental effects of steroid use.
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Discussion
To no one's surprise, muscle tissue is specialized to contract, to
become shorter. In this way, muscles move the bones they are attached to.
However, excitability, extensibility and elasticity, also number among the
characteristics of muscle tissue.
There are three different types of muscles (see Table 10.2) that can
be distinguished on the bases of voluntary versus involuntary control,
striated versus non-striated, location, fiber shape and number of nuclei.
Skeletal muscle is sometimes called voluntary muscle because we have
conscious control over it. But there are many important motor activities
that we do not consciously control. Most of us know that we do not have to
consciously think to make our hearts (cardiac muscle) beat (a good thing,
too, since I'm very forgetful). But involuntary muscle (smooth muscle) also
lines the small intestine and its contractions help us digest food.
Involuntary muscle (smooth muscle) lines the walls of many medium-
sized and small arteries and its contraction (and relaxation) helps regulate
blood flow to certain areas of the body. We will spend most of this lesson
focused on skeletal muscle.
Skeletal muscles move the skeleton and are what most people think
of as muscles. Most skeletal muscles have two attachments (or more)
between bones and the contracting muscle. The muscle is referred to as
the belly or gaster. The attachment that moves is called the insertion; the
stable attachment is the origin.
People are also sometimes surprised to learn that muscle tissue
proper contains connective tissue. The primary connective tissue
components are illustrated in Figure 10.1. Endomysium surrounds each
muscle cell (also called a muscle fiber). Perimysium surrounds a group of
muscle cells, called a fascicle. Finally, epimysium surrounds the entire
muscle. These three layers of connective tissue converge on the
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attachments of muscle to bone and actually become a cord of connective
tissue called a tendon.
The important thing to remember when looking at the structure of a
muscle cell is to understand when you are looking at a cell and when you
are looking at something inside a cell. A muscle fiber and a muscle cell are
one and the same thing, though this can be somewhat confusing. Look for
the endomysium because you know that it surrounds one cell at a time.
Like any other cell, a muscle fiber (see Figure 10.4 and 10.6) is
covered by a cell membrane, known as a sarcolemma. However, muscle
cells are usually studied in smaller functional units. These functional units,
called sarcomeres, can be thought of in the same way as any other
intracellular organelle. (Precisely speaking, sarcomeres are not organelles.
But it makes sense to think about them as organelles because then you
know you are looking at something inside a cell and not looking at the
outside of a cell.) A sarcomere is pictured in Figure 10.4d. Sarcomeres are
defined as running from Z line to Z line and contain the contractile
proteins (myofilaments) that result in the shortening of the muscle proper
and the production of movement. There are thick myofilaments (myosin)
and thin myofilaments (actin), which you can see in Figure 10.4. Together,
the Z lines, thick myofilaments and thin myofilaments, overlap
intermittently to form three areas or bands. There is an I band, and an A
band and an H zone. In a relaxed state the following are true (see Figure
10.7):
a. I bands contain thin myofilaments only,
b. the A band contains thick and thin myofilaments,
c. and the H zone contains only thick myofilaments.
The sliding filament theory of contraction (see Figures 10.7 and
10.8) hypothesizes that proteins within the thick and thin myofilaments
articulate to form "cross-bridges" with one another and pull the Z lines of
the sarcomere closer together. Said another way, the thin myofilaments of
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a sarcomere move inward, toward one another during contraction.
Multiplied many times in many sarcomeres through a muscle, the result is
observable contraction (shortening) of the muscle and movement. Now
study Figures 10.7 and 10.8 and deduce what happens to the A and I bands
and H zone after contraction.
A neuromuscular junction is crucial to muscle contraction. It
represents the meeting place of nerve and muscle tissues, the place where
the nervous impulse (command to contract) is actually given to the muscle
as a chemical message. Figure 10.9 shows the structure of a
neuromuscular junction. Note the components of the neuromuscular
junction. The chemical message or command is contained within synaptic
vesicles in the nerve fiber. When a nervous impulse reaches the end of the
nerve fiber, it causes the vesicles to release their chemical message in the
form of a neurotransmitter. The neurotransmitter then crosses the
synaptic cleft to bind with the sarcolemma (muscle cell membrane) to
stimulate the muscle fiber. Neurotransmitters differ depending upon the
tissue type, but the neurotransmitter for skeletal muscle is acetylcholine.
A motor unit consists of a motor neuron (motor nerve cell) and all
of the muscle cells it stimulates. There are gross and fine motor units.
Gross motor units have one neuron innervating many muscle cells (up to
several hundred), whereas fine motor units have far less muscle cells
innervated by a motor neuron (ten and sometimes less). Fine motor units
are found in areas where precise movement is required, such as the hands,
the face, and muscles of speech. Muscles responsible for large or gross
movements, like running or jumping, tend to have gross motor units
(muscles of the back, trunk, thighs, and legs).
Muscle tone (not to be confused with an isometric contraction) is
the state of partial contraction assumed by skeletal muscle. Tone confers
resilience on a skeletal muscle. But the number of muscle fibers in the
muscle that are contracting is not enough to produce observable
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movement. Muscle tone is essential to maintaining good posture because
it usually amounts to holding the position of the body steady while other
parts work (e.g., hands and upper extremities).
Muscle tissue is not often affected by pathology, though it is often
the site of relatively minor injury (strains, cramps). Some disorders of
muscles cause a decrease in muscle size, called atrophy, because of a loss
of contractile units within a muscle fiber. Muscular dystrophy, for
example, is an inherited disorder of muscle tissue which causes a
progressive loss of contractile units in muscle, with replacement by fat and
connective tissue. However, pathology is not the only cause of atrophy in
the muscle system; simple disuse, lack of exercise, will also result in
atrophy.
Unlike muscular dystrophy, myasthenia gravis affects the neuro
muscular junction. Anti-bodies produced by the individual block
transmission of a nerve impulse at the neuromuscular junction causing
weakness and early fatigue.
Fibromyalgia is sometimes called arthritis of the muscle system. Its
symptoms include pain over numerous "tender points" across the body.
The patient is also plagued by sleep disturbance, often accompanied by
depression.
Unfortunately, social pressure on youth often leads to drug abuse in
an effort to increase the strength of a muscle. Although a muscle will get
larger (hypertrophy) and stronger in response to exercise, use of steroids
(synthesized testosterone-like substances) will cause hypertrophy as well.
Serious physical complications associated with steroid abuse present
significant danger (see page 254).
Sample Questions
1. Name the property that gives muscle tissue the ability to receive and respond to stimuli.
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a. contractility b. excitability c. elasticity d. extensibility
2. Name the stationary attachment of a muscle.
a. tendon b. aponeurosis c. origin d. insertion
3. What is the connective tissue component of skeletal muscle that
surrounds a muscle fascicle? a. perimysium b. epimysium c. endomysium d. tendomysium
4. The term motor unit is applied to this.
a. connective tissue coverings around a muscle b. the union of a muscle's tendon with the periostium of bone c. a motor neuron and the muscle fibers it stimulates d. the triad of a skeletal muscle fiber
5. This portion of a sarcomere contains thick myofilaments only.
a. A band b. I band c. H zone d. Z line
Answers to Sample Questions
1. b; 2. c; 3. a; 4. c; 5. c
Go on to Lesson 11.
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Lesson 11 Muscle System
Reading Assignment
Read Chapter 11 in your textbook. As with the past few chapters
now, you will find Chapter 11 involves more studying of figures than actual
reading. Also, as before, I strongly urge you to take the time to learn the
objectives very well.
Objectives
By the end of this lesson, you should be able to:
1. Define muscle (ms.) actions: agonists (synergists), antagonists,
fixator.
2. Define first, second, and third class levers, noting placement of
fulcrum, resistance, and effort along lever arm. (Figure 11.2)
3. Identify (visually) and know the general attachments and primary
(usually angular) actions for the following ms.:
a. Muscles that move the vertebral column: rectus
abdominis, quadratus lumborum, external abdominal
oblique, internal abdominal oblique, psoas major, iliacus,
erector spinae group (iliocostalis, longissimus, spinalis). See
Figures 11.11 and 11.13.
b. Muscles of the abdominal wall: external abdominal
oblique, internal abdominal oblique, transversus abdominis,
rectus abdominis. See Figure 11.13.
c. Muscles of respiration: diaphragm, external intercostal,
internal intercostal. See Figure 11.12.
d. Muscles that act on the head: Sternocleidomastoid,
semispinalis capitis, splenius capitis, longissimus capitis,
trapezius. See Figure 11.11.
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e. Muscles that act on the pectoral girdle: pectoralis
minor, subclavius, trapezius, levator scapulae, rhomboideus
minor, rhomboideus major, serratus anterior. See Figure
11.15.
f. Muscles that move the humerus: pectoralis major,
latissimus dorsi, deltoid, teres major, supraspinatus, teres
minor, infraspinatus, coracobrachialis, subscapularis. See
Figure 11.16.
g. Muscles that act on the forearm: biceps brachii,
anconeus, brachialis, triceps brachii, brachioradialis,
supinator. See Figure 11.16.
h. Muscles of the forearm that act on the wrist, hand,
and digits: flexor carpi ulnaris, flexor carpi raidalis,
palmaris oongus, flexor digitorum superficialis (superficial
digital flexor), flexor digitorum profundus, flexor pollicis
longus, abductor pollicis longus, extensor pollicis longus,
extensor pollicis brevis, extensor digitorum, extensor carpi
radialis longus, extensor carpi radialis brevis, extensor carpi
ulnaris, pronator teres, pronator quadratus. See Figures 11.17
and 11.18.
i. Intrinsic muscle of the hand: abductor pollicis brevis,
flexor pollicis brevis, opponens pollicis, adductor policis,
lumbricals, palmar interossei, dorsal interossei, abductor
digiti minimi, flexor digiti minimi, opponens digiti minimi.
See Table 11.14 and Figure 11.19.
j. Muscles that move the thigh: psoas major, iliacus,
pectineus, gluteus maximus, gluteus medius, gluteus
minimus, tensor fasciae latae, adductor magnus, adductor
longus, adductor brevis, gracilis, rectus femoris,
"hamstrings," sartorius. See Figures 11.20, 11.21.
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k. Muscles that move the leg: sartorius, quadriceps femoris,
(vastus intermedius, vastus lateralis, rectus femoris, vastus
medialis), "hamstrings" (semimembranosus,
semitendinosus, biceps femoris), gastrocnemius. See Figures
11.20 and 11.21.
l. Muscles that move the ankle, foot, and toes: tibialis
anterior, extensor digitorum longus, extensor hallucis
longus, peroneus tertius, gastrocnemius, soleus, tibialis
posterior, flexor digitorum longus, flexor hallucis longus,
peroneus longus, peroneus brevis. See Figures 11.22, 11.23
and 11.24.
4. Describe most body movements as activities of groups of muscles
by explaining the roles of agonists, and antagonists.
Discussion
You have probably already deduced that the muscular system
should be entitled more specifically "the skeletal muscular system"
because the lesson involves exclusively those muscles that produce
observable and voluntary movement. So any use of the word "muscle" in
this lesson means skeletal muscle.
Analysis of muscle actions involves a set of terms used to describe
what a muscle is doing at a particular time, during a particular movement.
An agonist refers to the muscle(s) doing the work and shortening. The
antagonist is the muscle that must relax in order for the movement to
occur. The antagonist will usually produce the movement that is the exact
opposite of the movement produced by the agonist. As you work your way
through the objectives on specific muscles, try to think in terms of group
actions and the muscles that are agonists and antagonists. Concentrate on
flexion/extension, abduction/adduction and rotation. Muscles that
produce the same action are also said to be synergists.
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Figure 11.2 illustrates the three different types of levers: first,
second and third class. Analogies to a see-saw, wheelbarrow, and lifting an
object with tweezers are provided. Note that the most common type of
lever is the third class. Further note that third class levers are at a
mechanical disadvantage, but are well designed for rapid movement over
an extensive range of motion (as in running or throwing).
I would advise that you tackle the list of muscles you see in
Objective 3 in a logical manner. First, try to identify the major muscles in
Figure 11.7. Most people think it is helpful to study: 1. muscles acting on
the trunk and axial skeleton, 2. muscles of the shoulder girdle and upper
extremity, 3. muscles on the pelvic girdle and lower extremity. After you
can identify the muscles listed in the objectives, then start to study the
appropriate figures and accompanying tables. Try to construct logical
groupings of muscles that perform the same action. This will ease your
load.
Some clarifications:
1. You do not have to know all of the specific muscles of the erector
spinae; just remember it as one muscle with three parts: the lateral
iliocostalis group, the intermediate longissimus group, and the
medial spinalis group.
2. Some muscles are noted several times because they produce actions
at more than one joint (e.g., psoas major). Muscles that act on the
axial skeleton are particularly likely to fall into this category.
The other tip I give you is to make your own muscle flashcards.
True, there are very attractive commercial alternatives and even computer
software that will help you rehearse. But the advantages to making your
own are several. First, I believe you will learn a great deal from the act of
making your own flashcards; you get that extra mental rehearsal when you
construct your own flashcards. Second, it is a lot cheaper to make your
own flashcards. All you need are some index cards. Third, you can pass
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them down to your children when they come of age. (Just kidding on the
last advantage.)
Begin by listing the name of the muscle in the top left corner of the
index card. Then, write down the actions and attachments (origin,
insertion) of the muscle under the name. Leave a little room on the left
margin. This is where I write down the number of actions for the muscle.
Then, when I quiz myself, I can cover over the actions and know that I
must come up with one, two, three or more actions. Remember
attachments in general.
Let us try an example for the biceps brachii muscle. If you look up
the muscle, you will find that it has two primary actions (flexion of the
forearm, and supination), two origins and one insertion. Hence, I would
write the number "2" in the left margin for two actions to remember. For
our purposes, the general attachments to remember are scapula
(origin) to forearm/radius (insertion). You do not need to remember the
specific landmarks for attachments on bones. When it comes time to
study, I cover everything on the card except the name of the muscle and
the number I placed in the left margin. In this case, I know I must name
two actions.
Remember to identify the muscle as well on Figure 11.7. I could
always ask you facts about the muscle's location. For the biceps femoris I
could ask: "Is the muscle located on the posterior surface of the thigh?" "Is
the muscle superficial or deep?" "Is the muscle found in the lower
extremity?" or "Is the biceps femoris seen on a superficial view of the
posterior thigh?"
With regard to actions, think first mostly in terms of angular
motions (flexion/extension and abduction/adduction) or rotation; or
hybrids of angular movements or rotation (dorsiflexion, pronation, etc.).
Hint: You will only find significant rotation at ball-and-socket and pivot
joints. Another hint: The actions of the muscles that move the foot are
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determined by where each muscle's tendon passes the ankle (those of the
anterior compartment dorsiflex; those of the lateral and posterior
compartments plantarflex). Third study hint: Try to get a sense for
whether a muscle is deep, intermediate, or superficial, relative to other
muscles. This exercise will make subsequent identification of muscles
considerably easier. Remember your self-tests; all it takes is a photocopy
and discipline. Final hint: As a general rule of thumb, in the anatomical
position, muscles on the anterior parts of the neck, arms, forearms, chest,
and abdomen are flexors. Muscles on the anterior aspect of the thigh are
extensors (of the knee). Muscles on the posterior aspect of the neck, arms,
forearms, back, and buttocks are extensors. Muscles on the posterior
portion of the thigh are flexors. (Some muscles act on more than one joint:
take special note of these as well.)
Sample Questions
1. Name the muscle from the list below that is antagonistic to plantor flexion of the foot. a. peroneus brevis b. soleus c. tibialis anterior d. flexor hallucis longus
2. What is the name of a muscle that performs the desired action?
a. antagonist b. agonist c. synergist d. fixator
3. What is the primary action of the palmar interossei?
a. adduct digits b. flex digits c. abduct digits d. extend digits
4. This muscle turns the palm upward or anterior.
a. fibialis anterior b. plantaris
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c. adductor longus d. supinator
5. Which muscle below is not innervated by the obturator nerve?
a. sartorius b. adductor longus c. gracilis d. adductor magnus
Answers to Sample Questions
1. c; 2. b; 3. a; 4. d; 5. a
Written Assignment #4
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Identify muscles that produce flexion at the hip and their
antagonists. Identify muscles that produce abduction at the hip and
their antagonists..
2. Identify the lever type (first, second, or third class) in effect in
flexing the leg at the knee. Next, identify agonists and antagonists
to flexion of the knee.
Examination #2
Examination #2 follows written assignment #4. This will be a one-
hour, supervised examination. No books, notes, or other aids may be
brought to the exam. The examination consists of forty multiple-choice
questions of the same type you have seen in the sections of sample
questions in each lesson. The exam questions are allocated according to
the number of objectives per topic.
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Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
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UNIT 4 INTEGRATION
Lesson 12 Nervous Tissue
Lesson 13 Central Nervous System
Lesson 14 Peripheral Nervous System
Written Assignment #5
Lesson 15 Autonomic Nervous System
Written Assignment #6
Lesson 16 Special Senses
Lesson 17 Endocrine System
Examination #3
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Lesson 12 Nervous Tissue
Reading Assignment
Read Chapter 12 in your textbook. As this is the beginning of the
second half of the course, I remind you to use the objectives to guide your
reading.
Objectives
By the end of this lesson, you should be able to:
1. Define peripheral and central nervous systems. List the functions of
the nervous system. Classify spinal cord, brain, spinal nerves and
cranial nerves into either peripheral or central nervous system.
Define and distinguish somatic afferents, somatic efferents, visceral
afferents and visceral efferents (Figure 12.3).
2. Classify gray matter versus white matter in the CNS and PNS:
nerve, nucleus, ganglion, and tract.
3. State the general functions of supporting cells/neuroglial cells:
astrocyte, ependyma, oligodendrocytes, and microglia. See Figure
12.12.
4. Define and describe the general features of a typical neuron.
Include the following: dendrite, axon, cell body (perikaryon),
neurolemmocyte (Schwann cell), neurolemmal sheath, myelin
neurofibral node (know Figure 12.4). Also, contrast unipolar
(sensory neuron) (Figure 12.10c). and multipolar (motor neuron)
neurons (Figure 12.10a).
5. Define myelin, know the cells responsible for myelination, and state
the functional significance of myelin. See Figures 12.14 and 12.15.
6. Draw and explain a simple reflex arc (Figure 12.17), identifying its
five components.
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7. Define the connective tissue components of a (peripheral) nerve:
epineurium, perineurium, and endoneurium. See Figure 12.16.
8. Generally describe the components of a synapse: presynaptic
neuron, postsynaptic neuron, synaptic cleft, axon terminal, synaptic
vesicles, neurotransmitters (Figure 12.8).
9. Define and describe multiple sclerosis.
Discussion
A vital point about the nervous system that few books bring out is
no matter how you label and divide the nervous system for study, it is a
continuous entity (see Figure 12.2). Everything is connected! Even
though we might be studying the peripheral nervous system at one time,
the spinal cord at another, and the brain at yet another, the student should
not think the spinal cord is somehow separated from or not connected to
peripheral nerves and the brain. So as you work through the material, keep
this idea tucked away in the back of your mind. It will help you get the "big
picture" and formulate a better understanding of how the entire nervous
system works as one functional unit.
For convenience, the nervous system is often divided into the
central nervous system (CNS) and the peripheral nervous system (PNS).
The central nervous system is all nervous tissue found inside of bone—the
vertebral canal of the vertebral column and the inside of the skull or
cranium. The peripheral nervous system (PNS) is nervous tissue found
outside of bone; basically, everything else.
Nerve cells (neurons) are divided into sensory (afferent) and motor
(efferent). The afferent system is responsible for getting sensory
information to the CNS. The efferent system is responsible for getting
nervous impulses from the CNS to effector organs (like muscles, glands,
smooth muscle in the digestive system, etc.) (see Figure 12.3).
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The efferent (motor) system is further divided according to whether
the neuron innervates a voluntary (skeletal) muscle, or innervates an
involuntary (smooth or cardiac) muscle. The former system is referred to
as the somatic motor system; the latter is called the visceral motor system.
Later, specifically in the lesson on the autonomic nervous system, we will
discuss at length the differences between somatic motor and the visceral
(autonomic) motor systems.
Let's look at a more detailed rendering of the afferent and efferent
systems. The following is a functional classification based on the
direction an impulse is transmitted along nerve cell processes. Sensations
are carried toward the CNS for interpretation and can come from two
sources: sensory impulses coming from organs and blood vessels (referred
to generally as viscera) are carried by visceral sensory fibers and sensory
impulses from about everywhere else in the body (soma means "body") are
conducted along somatic sensory fibers. Motor commands are carried
away from the CNS toward effector organs (muscles) and are classified
according to the type of muscle innervated. If the axon leads to a voluntary
(skeletal) muscle, the neuron is a somatic motor. If the fiber leads to an
involuntary (cardiac or smooth) muscle, it is known as a visceral motor.
As you progress through Chapter 12, you will find a great variety of
cell types. Before you identify the parts of a typical neuron, however, you
should be aware of a category of cells found interspersed among nervous
tissue that are not actually nerve cells. The general title given to this
category of cells is neuroglia. Neuroglial cells assist nerve cells but do not
actually conduct nervous impulses. They support and protect nerve cells as
well as form myelin, a sheath of tissue that surrounds most of the length of
a neuron's axon and/or dendrite and increases the conduction velocity of a
nerve cell. Neuroglial cells are illustrated in Figure 12.12.
The second category of cells found in nervous tissue consists of
nerve cells also called neurons. We will use the neuron diagrammed in
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Figure 12.4 as our typical neuron to identify the component parts of a
nerve cell. Neurons can assume different shapes and sizes, but they all
pretty much have the parts labeled in Figure 12.4. Study Figure 12.4 and
identify the parts listed in Objective 4. Note, 12.4 actually shows two cells,
the motor (efferent) neuron and a neurolemmocyte (Schwann cell). As it
so happens, the motor neuron pictured is found in the anterior gray matter
of the spinal cord. The neurolemmocyte (Schwann cell), however, is found
in many places throughout the nervous system. The neurolemmocyte is
one of several types of neuroglia. It happens to produce myelin which
coats the processes (axons or dendrites) of some neurons.
Just a couple of remarks before we move on:
1. Note: the processes that extend into the periphery as axons and
dendrites are as much a part of the nerve cell (neuron) as the cell
body.
2. Note: the cell that lays down myelin along the length of a nerve
fiber (axon or dendrite) leaves spaces or gaps; these are called
neurofibul nodes (Node of Ranvier).
Returning to Figure 12.4 for a moment, axons from this type of
motor neuron actually compose the somatic portion of the efferent/ motor
system.
Now recall the point I made earlier—although the nervous system
and nervous tissue can be segregated to help us study, it is anatomically
continuous. For instance, the cell body and dendrites of the neuron you
see in Figure 12.4 are typically found within the CNS, but its axon is
usually in the PNS. The axon of the motor neuron in 12.4 is actually the
processes of the neuron that innervates muscle cells. (See the discussion
pertaining to a neuromuscular junction in the muscle tissue lesson.)
A special category of neurons are interneurons (association
neurons). These cells are found in between sensory and motor neurons.
They are also contained entirely within the CNS (brain or spinal cord);
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their axons do not lie outside the CNS as those of sensory and motor
neurons. You do not have to know any particular types of association
neurons, but you should know of them and their function in a conceptual
sense. Technically, all of the neurons of the brain are various types of
association neurons.
Commonly, you will read or hear of white matter and gray matter of
the nervous system. White matter and gray matter are additional ways in
which you can talk about certain parts of the nervous system, different
ways of talking about some of the same structures found in the nervous
system.
I have waited until after the explanation of myelin to discuss gray
matter and white matter because the discussion of myelin was a necessary
pre-requisite. In the simplest terms, white matter appears white or light
colored because it contains axons and dendrites that are myelinated. The
lipid material of myelin confers a lighter hue on some nerve tissue we
designate as white matter. Gray matter is darker in coloration because it
does not contain myelinated axons or dendrites.
In summary, white matter contains myelinated axons or dendrites.
Gray matter contains unmyelinated axons and dendrites and cell bodies
of neurons (which are never myelinated). White matter and gray matter
are further designated depending on whether you find it in the PNS or the
CNS.
White matter in the PNS is designated as a "nerve," while in the
CNS it is called a "tract." Importantly, in both cases what you find in the
white matter is the same—myelinated axons and dendrites. Gray matter in
the PNS is called a "ganglion"; in the CNS it is referred to as a "nucleus."
You will find that these terms will be used more often as you
progress through the chapters on the nervous system. Try not to be
intimidated by the jargon. Sometimes we just use more specific
terminology to refer to structures in order to be more precise. But always
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keep in mind, no matter what kind of "matter" we are talking about, no
matter what part of the entire nervous system we are talking about, it all
amounts to either cell bodies, axons (myelinated and unmyelinated), and
dendrites (myelinated and unmyelinated).
Like muscle, nerves have connective tissue for support. Just as we
saw that muscle tissue has connective tissue components, so too, if you
study Figure 12.16, you will find that nerves include connective tissue
components. The prefix actually tells you what structure(s) the connective
tissue surrounds. For instance, just as endomysium surrounds each
individual muscle cell, the endoneurium surrounds each individual nerve
fiber (axon or dendrite) in the nerve. If the analogy holds, the following
should also be true:
1. perineurium surrounds a group (called fascicle) of nerve fibers in a
nerve,
2. and epineurium surrounds the entire nerve.
Study Figure 12.16 and decide for yourself whether this is the case
or not.
In studying Figure 12.8, much of the terminology should seem
pretty familiar to you. Can you remember where you have seen these
structures before? If you remembered the neuromuscular junction we
studied in the muscle tissue lesson, then terms like axon terminal, synaptic
vesicles, synaptic cleft, and neurotransmitters should be recalled. The
major difference between a synapse and neuromuscular junction is that
the synapse is between two neurons, whereas the neuromuscular junction
is between a nerve cell and a muscle cell. Neurotransmitter receptors on
the postsynaptic membrane receive the neurotransmitter substances after
they have crossed the synaptic cleft. These are not unique to the synapse;
neurotransmitter receptors are also present on the postsynaptic
membrane of the neuromuscular junction.
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Synapses work in only one direction. The presynaptic and
postsynaptic membranes are always the same at any given synapse. Hence,
nervous impulses can travel in only one direction. You do not have to
know specific transmitter substances.
Although "thinking" as we customarily know it occurs only in the
brain, the spinal cord can do a few things on its own. These tasks are called
reflexes because they happen automatically. Take note of the five
components of a reflex arc and Figure 12.17.
For example, imagine that you prick a finger with a pin. The pain
receptor senses "pain," then the impulse is transmitted along a sensory
neuron to an interneuron in the spinal cord. The final part of the arc
consists of the motor neuron sending an impulse to the effector (in this
case a skeletal muscle) to remove your finger from the pin. Get the
"point"? (A little anatomy humor.) This happens automatically, without
conscious thought, and is totally controlled by the spinal cord. Hence, we
call it a spinal reflex.
Multiple sclerosis is a neurological disorder in which the myelin
sheaths surrounding nerve fibers in the CNS deteriorate. It is thought to be
an autoimmune disorder and is more common in temperate climates. The
disorder progresses at different rates in different individuals. Sometimes
initial symptoms subside and the person will be asymptomatic from then
on. More commonly, the disorder progressively worsens with each "attack"
(exacerbation), causing progressively more impairment. Typical symptoms
include blurred vision, slurred speech, muscle weakness/fatigue, balance
difficulties, incontinence, and depression.
Sample Questions
1. This name is given to a neuron that transmits a nerve impulse to the CNS. a. motor b. sensory
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c. bipolar d. interneuron
2. Which cell does not belong with the others because of its function?
a. sensory neuron b. Schwann cell c. motor neuron d. interneuron
3. This portion of the nervous system is usually considered to be
involuntary. a. central b. somatic c. visceral d. peripheral
4. These nerve fibers convey impulses to skeletal muscles.
a. somatic motor b. visceral sensory c. somatic sensory d. visceral motor
5. Name the junction between two neurons.
a. neuromuscular junction b. motor end plate c. hillock d. synapse
Answers to Sample Questions
1. b; 2. b; 3. c; 4. a; 5. d
Go on to Lesson 13.
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Lesson 13 Central Nervous System
Reading Assignment
Read Chapter 13 and answer the objectives listed below. As before,
pay closer attention to the material associated with the objectives.
Objectives
1. Identify ventricles, interventricular foramina, cerebral aqueduct,
arachnoid villi, choroid plexus, median aperture, lateral aperture.
Explain the formation of cerebrospinal fluid. Define the different
layers of the meninges: dura mater, arachnoid, and pia mater. See
Figures 13.4b, 13.11, 13.30, and 13.32.
2. Identify the gross features of the cerebrum: hemispheres, corpus
callosum, central sulcus, lateral sulcus, longitudinal fissure,
transverse fissure, cerebral cortex, gyri, and sulci (Figures 13.20).
3. Identify the lobes of the cerebrum and the general functions of each
(Figure 13.23).
4. Describe the three types of white matter in the cerebrum and the
general connections established by each: association fibers,
commissural fibers (corpus callosum), and projection fibers
(internal capsule) (Figure 13.26).
5. Identify the components of the basal ganglia/nuclei and its general
function (Figures 13.21 and 13.27).
6. Discuss the significance of cerebral dominance for language. Also
state implications of damage to the areas involved in language
(Auditory association area, Broca's [motor speech] area, arcuate
fasciculus).
7. Identify the thalamus and state its functions (Figures 13.16, 13.17
and 3.18).
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8. Identify the hypothalamus and state its general functions (Figures
13.16 and 13.19). Also, identify the pituitary gland and
infundibulum (pituitary stalk).
9. Identify the main components of the brainstem and connections
with the cerebellum. Specifically, for the midbrain, state the
functions of the superior colliculi, inferior colliculi, red nucleus,
cerebral peduncle, and substantia nigra. In the pons, state the
functions of the pneumotaxic area, apneustic area, and pontine
nuclei. For the medulla, state the functions of cardiac, vasomotor,
respiratory centers, and the "pyramids." See Figures 13.13 and
13.14.
10. Define the reticular formation in the brainstem and state its
functions (Figure 13.29).
11. Identify the anatomy and the functions of the cerebellum, defining
the components of the cerebellar peduncles (Figure 13.15).
12. Describe the gross features and extent of the spinal cord: cervical
and lumbar enlargements, conus medullaris, filum terminale, and
cauda equina (Figure 13.2).
13. Describe and draw a cross section of the spinal cord identifying:
central canal, white matter, gray matter, anterior, posterior and
lateral horns, anterior, posterior and lateral funiculi, gray
commissure, anterior median fissure, and posterior median sulcus
(Figure 13.4 and 13.5).
14. Know general function and location of sensory and motor tracts in
the spinal cord (see Tables 13.6, 13.7, Figure 13.34).
15. Know these clinical applications: effects of spinal cord section at the
level of the cervical enlargement and between cervical and lumbar
enlargements; stroke.
16. Locate the limbic system and define its functions (13.28).
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Discussion
Read Chapter 13 to get oriented. You should know that the brain is
comprised of four parts: the cerebrum, brain stem, diencephalon, and
cerebellum. The entire central nervous system (CNS) is protected by the
meninges.
Three layers of meninges cover and protect the entire CNS. They are
comprised of: an outer tough layer—dura mater; a middle layer—
arachnoid; and an inner, delicate membrane that adheres directly to the
spinal cord and brain—pia mater. The subarachnoid space contains the
cerebral spinal fluid (CSF). This fluid helps protect the spinal cord by
providing a fluid shock absorber to dissipate external blows to the
vertebral column. You can see all of these meningeal structures in Figures
13.4b, 13.11, 13.30 and 13.32.
You should also recognize the dura mater, arachnoid, and pia mater
also cover the brain. These coverings continue throughout the CNS. Figure
13.11 identifies ventricles that are part of the cerebrospinal fluid (CSF)
circulation system. CSF is produced by capillary networks called choroid
plexuses, located in each of the four major ventricles (two lateral, a third
and a fourth).
Three apertures (one median, two lateral) in the fourth ventricle
give CSF access to the subarachnoid space. The CSF moves from the
ventricles into the subarachnoid space and then is returned to the venous
system by dural sinuses (see Figure 13.30). A dural sinus is a venous
channel running through the dura mater. Notice in Figure 13.30a that the
superiorly-directed projections push through the sinus as arachnoid villi
(villus is singular). The arachnoid villi are responsible for returning the
CSF back into the bloodstream. Therefore, CSF circulation begins in the
choroid plexuses of each ventricle where CSF is produced. The CSF finds
its way into the subarachnoid space via one of the three apertures (Figure
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13.11). After a time, the CSF is returned to the bloodstream by way of one
of the arachnoid villi associated with the superior saggital sinus (Figure
13.30).
The cerebrum is the part of the brain most people think about or
picture when the word brain is used. Like the rest of the CNS, the
cerebrum is comprised of gray matter and white matter, except it is
arranged in a fashion just the reverse of that in the spinal cord. The gray
matter (cell bodies mostly) is situated on the outside of the cerebrum; this
area is referred to as the cortex (see Figure 13.23). Study the cerebrum in
Figure 13.20 to identify the structures listed in Objective two.
The white matter (primarily myelinated axons) of the cerebrum is
underneath (deep to) the cortex. It contains three kinds of fibers (axons).
Association fibers connect different lobes on the same hemisphere.
Projection fibers include those axons from the thalamus (by way of the
internal capsule) on their way to the cortex. Projection fibers also include
fibers (axons) from cell bodies in the cortex on their way to the internal
capsule. Some of the projection fibers directed inferiorly eventually
become some of the descending tracts (the corticospinal tracts for
instance). The last type of fiber in the white matter of the cerebrum is
called a commissural fiber. Commissures connect the two hemispheres of
the cerebrum. Study Figure 13.26 to get a sense of what areas the axons of
the white matter of the cerebrum connect. There are anterior and posterior
commissures as well as the largest commissure—corpus callosum. Corpus
callosum is labeled in Figure 13.26.
Figure 13.23 displays a functional map of the cerebral cortex. Be
able to define the general functions of each lobe of the cerebrum. To make
your task a little easier, note that motor areas are confined to the frontal
lobe, whereas sensory areas are found on temporal, parietal, and occipital
lobes. Below is a matching exercise to test your recall after you have
studied the cortical areas of the cerebrum for a while.
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Identify one correct answer for each question.
a. frontal lobe b. temporal lobe c. occipital lobe d. parietal lobe
1. Receives sensory impulses from the eyes and interprets shape and color. 2. This area of the brain receives sensory information from cutaneous,
muscular, and visceral receptors from various parts of the body. 3. Controls voluntary movements of the eye. 4. Controls muscles of speech by translating thoughts into speech. 5. Voluntary control of skeletal muscle, usually on the opposite side of the
body.
Read on for the answers.
The basal nuclei represent a loose coalition of separate nuclei
controlling gross subconscious movements and muscle tone. Swinging of
the arms while walking and contraction of proximal limb musculature in
fundamental movement patterns (e.g., walking, throwing, etc.) are
controlled by the basal nuclei. The basal nuclei are also responsible for
starting and stopping movements. Some instructors liken the basal nuclei
to a "filtering" system because the characteristic sign of dysfunction of the
basal nuclei is involuntary (unwanted) movement (dyskinesia)—as in
Parkinson's disease. If the filter was working, the involuntary movements
would not sneak through.
Identify the parts of the basal ganglia/nuclei (caudate, lentiform
nuclei claustrum) in Figures 13.21 and 13.27. With the substantia nigra
(not pictured), these are major structures in the basal nuclei. (The answers
to the matching exercise are 1. c, 2. d, 3. a, 4. a, and 5. a.)
Proficiency with language, such as understanding the written and
spoken word and speech, are controlled by the so-called dominant cerebral
hemisphere. For most people, the dominant cerebral hemisphere is the
left. (Since cerebral control of the body is contralateral, the dominant
hemisphere usually is associated with the dominant or preferred hand).
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The auditory association area (see Figure 13.23) on the temporal lobe
receives and interprets auditory information (speech comprehension).
Association fibers (the arcuate fasciculus) connect the auditory association
area with the Broca's (motor speech) area on the frontal lobe. This allows
us to hear a question in class, and verbalize an answer to the question.
Damage to any of these structures will result in aphasia (difficulty
using and/or understanding written or spoken language). Note that
aphasia results only when there is damage to one of these areas on the
dominant cerebral hemisphere. This makes language unique because
most other cerebral functions are bi-lateral.
The thalamus is an aggregation of gray matter (nuclei) at the end of
the brainstem; the thalamus is the "gateway" to the cerebral cortex (see
Figures 13.16 and 13.18). Ascending (sensory) tracts travel superiorly
through the spinal cord, then continue on through the brainstem. Hence,
the thalamus relays most types of sensory information (except smell) to
the cerebral cortex via a thick band of fibers (axons), called the internal
capsule (see Figure 13.17b), from the thalamic nuclei.
Below the thalamus (see Figures 13.16 and 13.19) one finds a second
group of nuclei, called the hypothalamus. "Hypo" ("less than" or "under")
suggests the location of these nuclei, directly under the thalamus. The
hypothalamus has several major functions you should remember. It plays
a role in the autonomic nervous system as its major control center. The
hypothalamus also influences the endocrine system through its
communication with the pituitary gland via the infundibulum (pituitary
stalk), illustrated in Figures 13.16 and 13.19 (which we will study more in
the endocrine lesson). There are certain cyclical centers for hunger, thirst,
and sleep patterns. Body temperature is also regulated by hypothalamic
nuclei.
Together the hypothalamus and thalamus are called the
diencephalon.
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The continuation of the spinal cord upward is the brainstem (see
Figures 13.13 and 13.14). The brainstem lies on the ventral or basal surface
of the brain.
All of the parts of the brainstem share several major functions:
1. They act as a conduit for the ascending or descending tracts (in
other words, the brainstem connects the spinal cord to the rest of
the brain and parts of the brain with one another).
2. They house many of the cranial nerve nuclei.
3. They are the home for several other important nuclei, including the
reticular formation (discussed at some length below).
You should know that the brainstem is composed of three parts:
medulla, pons, and midbrain. Each has a connection with the cerebellum.
(Identify the cerebellum in Figure 13.15.). The connections are called
peduncles. The medulla, pons, and midbrain connect with the cerebellum
via inferior, middle, and superior cerebellar peduncles, respectively
(Figure 13.13c).
You should also know the following about each part of the
brainstem:
1. The medulla contains many important "centers" (Figure 13.14) for
vital functions (cardiac rhythm, respiratory rhythm, and blood
pressure). This is why damage to the medulla is often fatal. The
medulla also contains nuclei for cranial nerves 8, 9, 10, 11, and 12.
(Number 8 is shared with the pons.) The medulla is connected with
the cerebellum by the inferior cerebellar peduncle. See Figure
13.13c. The pyramids of the medulla carry motor fibers that
originate in the frontal lobe of the cerebrum, destined for the spinal
cord.
2. The pons also contains several cranial nerve nuclei and pontine
nuclei. The latter send axons to the cerebellum via the middle
cerebellar peduncle. See Figure 13.14. The pons contains nuclei for
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cranial nerves 5, 6, 7, and 8. The pons also helps regulate
respiration through apneustic and pneumotaxic centers.
3. The midbrain, likewise, contains nuclei for cranial nerves as well as
the red nucleus, substantia nigra, and corpora quadrigemina. The
red nucleus is the origin of the rubrospinal tract. The nuclei of the
superior and inferior colliculi serve as the origins for fibers that will
eventually become the tectospinal tract. The substantia nigra joins
several other widely separated nuclei to form a functional unit
called the basal nuclei. The midbrain also houses nuclei for the
third and fourth cranial nerves. See Figure 13.14.
Throughout the brainstem is another poorly organized collection of
nuclei called the reticular formation (see Figure 13.29). The reticular
formation is vital to our general level of alertness and attention. This is
why the reticular formation is sometimes called the reticular activating
system. The reticular formation also plays a role in controlling muscle tone
through its several reticulospinal tracts.
As you can probably tell by now, the cerebrum does not work alone.
We have already identified other parts of the brain, the thalamus and basal
ganglia especially, that play major roles in coordinating things. We need to
add the cerebellum to that list now.
Identify the cerebellum in Figure 13.15. Histologically, the
cerebellum is arranged in a fashion similar to the cerebrum, with cell
bodies (gray matter) on the outside and fibers (white matter) on the
inside. We already noted the cerebellum has three attachments
(peduncles), one with each part of the brainstem (see Figure 13.13c).
Through some of these peduncles, the cerebellum can send axons to
influence and help other parts of the brain do their jobs better.
The cerebellum is primarily a motor coordination center. This
means the cerebellum checks movements as they occur, to assure they are
carried off as planned, so the entire movement appears as one smooth
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whole. If a movement "error" is detected, then the cerebellum alerts other
parts of the brain, so the movement can be corrected. When things go
wrong with the cerebellum, you will sometimes observe a decomposition
of movements, movements which begin to appear short, choppy, and
uncoordinated—a conditions known as ataxia (uncoordinated movement).
The cerebellum is also concerned with control of postural muscles
and equilibrium. Along with its coordination functions, the cerebellum
does all of these tasks at the subconscious level. This is very useful because
it frees up attention and cerebral capacity to think about things far more
interesting than contracting the right muscles so that we can stand or sit
erect. The cerebellum makes life a lot more interesting because it takes
care of almost all of the tedious "work" without having to occupy a lot of
our conscious attention.
You should have a general familiarity with the components of each
of the three peduncles that connect the cerebellum to each part of the
brainstem. The inferior peduncle carries proprioceptive (joint sense)
sensation to the cerebellum. The middle peduncle carries fibers from the
pons to the cerebellum. The superior peduncle carries fibers to the red
nucleus from the cerebellum.
The spinal cord is primarily a pathway for nervous impulses to and
from the brain. It also performs a few simple, protective functions (called
spinal reflexes) on its own. Nevertheless, you should remember that
neurons in the spinal cord are largely under the control of neurons
residing in the brain. This is why some neurons in the spinal cord are
referred to as lower motor neurons (and those in the brain as upper motor
neurons).
Recall that the spinal cord and the remainder of the CNS is
comprised of white matter and gray matter. The gray matter marks the
location of nerve cell bodies and appears as a darker hue because the cell
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bodies of neurons are not myelinated. White matter is made up of
myelinated nerve cell processes—axons and dendrites.
The general features of the spinal cord are illustrated in Figure 13.2.
The spinal cord begins at the foramen magnum (of the occipital bone) and
ends at the level of upper lumbar vertebrae in a tapered structure called
conus medullaris. Inspect the length of the spinal cord proper and note
that it is not of uniform thickness throughout its entire length. Two areas
in particular are wider; they are called the cervical and lumbar
enlargements. What do you think accounts for these enlargements?
Filum terminale arises from the conus medullaris and anchors to
the coccyx. The filum terminale is not nervous tissue. It is, more or less, a
ligament that helps to secure and stabilize the spinal cord in the vertebral
canal. Filum terminale is found in amongst a series of fibers called cauda
equina.
Cauda equina is comprised of nervous tissue. Because the spinal
cord does not extend the entire length of the vertebral column, some nerve
fibers—those in the lumbar, sacral, and coccygeal regions specifically—
must travel inferiorly for a distance to exit at the appropriate vertebral
level. For example, the S1 spinal nerve will exit at the S1 vertebral level,
even though the spinal cord proper ends at about L2. To do this, S1 fibers
must travel downward until they arrive at the appropriate vertebral level.
This effect for lumbar and sacral spinal nerves results in the cauda equina.
Figures 13.4 and 13.5 shows the spinal cord in cross section. The
gray matter, where all the cell bodies are, forms an H-shaped
configuration in the center of the cord. Around the gray matter is white
matter, composed largely of myelinated axons. A gray commissure forms
the horizontal bar of the H in the gray matter. The H-shaped pattern is
also further subdivided into horns, two anterior, two posterior. The white
matter is likewise subdivided into anterior, lateral and posterior funiculi.
The word "funiculus" is used because the white matter contains bundles of
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myelinated axons carrying information up to or down from the brain. Soon
you will learn that each of the funiculi is further subdivided into ascending
or descending tracts. The ascending tracts are carrying sensory
information to the brain; the descending tracts are carrying motor
information to the spinal cord. (It is a good idea to test yourself on Figure
13.5; remember, part of the objective is to draw a cross section of the
spinal cord, too.)
The cell bodies of motor neurons are located in the anterior gray
horn of the spinal cord. The cell bodies of sensory neurons are located in
structures called a dorsal root ganglia—as a cluster of cell bodies in the
PNS. See Figure 13.5.
Just as nerves are white matter in the PNS, tracts are the white
matter in the CNS. Tracts, as we saw before, were defined as columns or
bundles of axons traveling up (ascending tracts) or down (descending
tracts) the spinal cord, to or from the brain. As it so happens, the
organization of tracts is not haphazard, but rather systematic. Axons
carrying similar kinds of impulses (or information) tend to group together
so that we may identify specific tracts carrying specific kinds of
information (sensory or motor). Study Tables 13.6 and 13.7 and Figure
13.34. You should know all sensory (ascending) tracts and motor
(descending) tracts, where they are located in the spinal white matter, and,
generally, what kind of functions they perform. You do not have to know
the reticulospinal tracts.
Many of the tracts are named for where they begin and end, so this
should make your task easier. For instance, the lateral spino-thalmic tract
is located in the lateral white matter of the spinal cord and carries
information from the spinal cord ("spino") to the thalamus ("thalamic") in
the brain. Even if you could not remember that it is an ascending tract, you
could deduce that it is an ascending tract from the name. Likewise,
spinocerebellar tracts go to the cerebellum from the spinal cord. And
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corticospinal tracts go from the cerebral cortex to the spinal cord (anterior
and lateral give locations of the corticospinal tracts in the white matter). It
might be a good idea to test yourself on the function of each tract by
developing a matching exercise. Put the tracts on one side and the
functions on the other, then try and match them up.
Injuries to the CNS are very serious and, too often, permanent.
Trauma to the spinal cord is usually from an external event—such as a
vehicular accident. Although, many different types of injuries may result.
Two of the most common result in paraplegia and quadriplegia. Severing
the spinal cord between cervical and lumbar enlargements denies
voluntary control to both lower extremities. Severing the spinal cord at the
cervical enlargement means that all four extremities are involved—
quadriplegia.
A cerebral vascular accident (CVA) or stroke is a form of brain
injury, making it similar in some respects to any brain trauma except for
etiology. The majority of strokes cause injury by depriving brain tissue of
blood supply (ischemia). In contrast, brain trauma may result from direct
injury to brain tissue, or more commonly, put pressure on brain tissue as a
result of a blood clot (hematoma) associated with damage to meningeal
blood vessels.
In either case, the symptoms are correlated with the extent of injury
and the nature of the damaged tissue. For example, CVAs that affect the
internal capsule (projection fibers) on one side often result in partial or
complete paralysis on the opposite side of the body (contralateral
hemiphagia). Furthermore, strokes to the dominant hemisphere
frequently result in difficulty using or understanding language (aphasia).
Cerebral palsy results when some event causes the fetal brain to be
deprived of an adequate oxygen supply before birth. Hence, cerebral palsy
is a congenital brain injury (in contrast to strokes and traumatic brain
injuries which are acquired). Cerebral palsy most commonly affects motor
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areas of the cerebral cortex, but may affect the basal nuclei or the
cerebellum. Symptoms manifest as syndromes of motor impairments,
such as spasticity of control, disruption of muscle tone and function,
ataxia, and other motor dysfunction
The limbic system is illustrated in Figure 13.28. It is generally
regarded as the primitive brain and comprised of nuclei that surround the
brainstem—primarily the amygdaloid nucleus, fornix, hippocampus, and
cingulate gyrus. The limbic system is primarily involved in primitive
emotions and, surprisingly, memory. Several structures in the limbic
system are subject to considerable research effort because deterioration of
some of the nuclei is associated with one type of senility/dementia
(Alzheimer's disease). Note also the involvement of the olfactory nerve in
the limbic system—a basis for the ability of perfume and after-shave to
provoke sex-drive.
Sample Questions
1. This structure serves as a relay for sensory information bound for the cerebral cortex. a. cerebellum b. thalamus c. midbrain d. basal ganglia
2. An obstruction in an interventricular foramen would interfere with
flow of CSF into this space. a. lateral ventricle b. third ventricle c. fourth ventricle d. median aperture
3. This lobe of the brain is responsible for controlling voluntary motor
activity. a. frontal lobe b. parietal lobe c. occipital lobe d. temporal lobe
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4. The pons is connected to the cerebellum by this band of white matter.
a. superior cerebellar peduncle b. decussation of pyramids c. tentorium cerebelli d. middle cerebellar peduncle
5. The vital centers for control of respiration, heart rate, and blood
pressure are located here. a. spinal cord b. medulla c. cerebrum d. cerebellum
Answers to Sample Questions
1. b; 2. b; 3. a; 4. d; 5. b
Go on to Lesson 14.
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Lesson 14 Peripheral Nervous System
Reading Assignment
Read Chapter 14 in your textbook. As always, study the figures
thoroughly and let the objectives guide your reading.
Objectives
By the end of this lesson, you should be able to:
1. List all twelve cranial nerves and the part of the brain or brainstem
associated with each. Briefly, describe the structures innervated by
each. Classify cranial nerves as primarily sensory, primarily motor,
or mixed. (See Tables 14.2, 14.3, and Table 2 in the Discussion
section of this lesson.) Also name the 31 pairs of spinal nerves
(Figure 14.6)
2. Describe the typical spinal nerve (see Figures 14.2 and 14.7), its
dorsal and ventral roots, and its dorsal and ventral rami. Discuss
the relationship between ventral rami and intercostal nerves and
plexuses. Identify body regions innervated by nerves from each
plexus.
3. Describe the concept of a plexus. Identify ventral rami of spinal
nerves that contribute to each plexus (see Figures 14.8–14.13 and
Tables 14.4–14.7). Know which plexus each of the following nerves
arise from and the muscular innervations of each nerve and plexus:
phrenic, ulnar, median, axillary, musculocutaneous, radial, femoral,
obturator, superior gluteal, inferior gluteal, tibial, peroneal
(fibular), pudendal.
4. Trace a nerve impulse from the spinal cord to the brachialis muscle;
note important anatomical structures and landmarks that the
impulse passes on its way to the brachialis muscle.
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5. Define dermatome and state its clinical importance (see Figure
14.14).
6. Describe the effects of peripheral nerve section to the following
nerves: radial, median, ulnar, femoral, tibial, peroneal (fibular).
Discussion
Inspect Figure 14.6. You will observe that there are 31 pairs of
spinal nerves. These are the nerves that emerge from the intervertebral
foramina. There are eight cervical, 12 thoracic, five lumbar, five sacral and
one coccygeal. Spinal nerves are named for the vertebrae below until the
eighth cervical spinal nerve (C8). C8 spinal nerve is between C7 vertebra
and T1 vertebra. (There is no C8 vertebra.) Once past C8, the naming
convention changes; spinal nerves from the first thoracic (T1) down are
named for the vertebra above their exit. This is why there are eight cervical
spinal nerves but only seven cervical vertebrae.
Study Tables 14.2 and 14.3. You have to know the general (and
most significant) functions of each cranial nerve and the areas of the brain
or brainstem the nerve originates from. Your book gives far more
information than you need to know, so I have summarized the information
you need to know in this course in Table 1 in this lesson. (You should still
read the material in the book, naturally.) I tend to use action words to help
remember functions. The cranial nerves should be thought of as twelve
additional pairs of spinal nerves for our purposes.
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Table 1. Cranial Nerves
Brain/ Brainstem Origin Cranial Nerve Function
CEREBRUM 1. olfactory smell 2. optic vision MIDBRAIN 3. oculomotor moves eye muscles, visceral
motor to pupil 4. trochlear moves eye muscles PONS 5. trigeminal moves muscles of chewing;
sensory to front of head 6. abducens motor to eye muscles 7. facial moves facial muscles (smiling,
etc.), tastes, salivates, cries PONS AND MEDULLA 8. vestibulocochlear hears, monitors balance MEDULLA 9. glossopharyngeal swallows, tastes, salivates,
monitors blood pressure 10. vagus swallows, tastes, some motor to
muscles of speech, parasympathetic, most of the ventral body cavity (viscera)
11. accessory turns the head (sternocleidomastoid muscle) and shrugs the shoulder (trapezius) muscles
12. hypoglossal moves the tongue
Next, consider Figures 14.2 and 14.7. The diagrams portray a spinal
nerve from formation to division into two branches, called rami. Spinal
nerves are formed when two roots, one ventral and one dorsal, come
together. The ventral root is motor; the dorsal root is sensory. Once the
two roots have jointed, you have a spinal nerve. From this point on, the
nerve is also considered a mixed nerve, mixed in the sense that it has
both sensory and motor components (fibers). After spinal nerves have
exited the intervertebral foramina, they split—one branch going forward,
one backward. These branches have names: the first is the ventral ramus,
the other one is the dorsal ramus. Do you think the rami are motor only,
sensory only, or mixed?
Dorsal rami innervate the muscles of the deep back (e.g., erector
spinae) and provide sensory innervation to the back. Verntral rami can do
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one of two things. They either become intercostal (between the ribs)
nerves or they enter into plexuses. There are four major plexuses.
A plexus is a network of nerves that begins with ventral rami. They
combine and recombine and eventually result in distinct nerves. Study of
Tables 14.4 through 14.7 and Figures 14.8 through 14.13. Identify muscle
groups innervated by each plexus (e.g., nerves from the brachial plexus
innervate muscles of the shoulder girdle and upper extremity and provide
sensory/cutaneous innervation of the upper extremity). Next, identify
muscle groups innervated by specific nerves and plexuses listed in
Objective #3. For example, the radial nerve innervates muscles of the
posterior arm and forearm (these muscles generally extend the forearm,
wrist, and digits).
Study each plexus and note the ventral rami of spinal nerves that
contribute to each. An unfortunate convention is that the ventral rami that
contribute to the formation of a plexus are called roots. The word "roots"
here does not refer to ventral and dorsal roots that combine to form spinal
nerves. Note—you do have to remember the nerves that arise from the
plexuses. (By the way—the answer to the question posed a couple of
paragraphs above is that ventral and dorsal rami are mixed. Any nerve
peripheral to the intervertebral foramen is mixed.)
To summarize, the cervical plexus is formed by ventral rami of
spinal nerve C1–5. The brachial plexus receives contributions from ventral
rami of C5–T1. The lumbar plexus is formed from spinal nerves L1–L4. L4
overlaps into the sacral plexus, which receives contributions from L4–S4
spinal segments. Remember to identify the nerves in Objective #3 and the
plexus of origin for each.
I have attempted to summarize and simplify nervous innervations
in Table 2.
Table 2. Nervous Innervations
Nerve Area
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Nerve Area Dorsal Rami Muscles of the deep back Phrenic Diaphragm Intercostals Intercostal muscles, muscles of the abdominal
wall Pectoral nerves Pectoral muscles Dorsal Scapular Rhomboids and levator scapulae Suprascapular Supraspinatus, Infraspinatus Thoracodorsal Latissimus dorsi Long Thoracic Serratus anterior Axillary Deltoid, Teres minor Ulnar 1½ muscles of the anterior forearm and intrinsic
muscles of the hand (all digits except thumb) Subscapular Subscapularis, Teres major Radial (includes branches
that become posterior interosseous nerve)
Muscles of the posterior arm and forearm
Musculocutaneous Muscles of the anterior arm Median Muscles of the anterior forearm and thumb Femoral Muscles of the anterior thigh Obturator Muscles of the medial thigh Inferior gluteal Gluteal muscles Superior gluteal Gluteal muscles Tibial (includes sciatic
innervations) Muscles of the posterior thigh and leg
Peroneal (fibular nerve) Muscles of the lateral and anterior leg Pudendal Perineum (floor of pelvis)
The fourth objective asks you to trace a nerve impulse from spinal
cord to brachialis muscle. If you understand this pathway, you should be
able to trace a nerve impulse from the spinal cord to any of the muscles
you learned in the muscle system lesson. The pathway to the brachialis
muscle is as follows:
Anterior gray horn of spinal segments C5–T1 to anterior roots of
spinal nerves C5–T1 to join posterior roots of spinal nerves C5–T1 to form
spinal nerves C5–T1 to ventral rami of spinal nerves C5–T1 to form "roots"
of brachial plexus. The impulse then negotiates trunks–divisions–cords of
the plexus to eventually form five terminal nerves of the brachial plexus
(among these is the musculocutaneous nerve, which innervates the
Brachialis muscle).
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As you might surmise, spinal cord damage is far more serious than
trauma to a single peripheral nerve. With the latter, only the muscles and
skin innervated by the damaged nerve will be affected. Review the clinical
applications in Chapter 14 that describe the motor impairment that would
result if median, ulnar, radial, femoral, tibial, or peroneal (fibular) were
damaged. Even if the damaged nerve is a major one, the extent of the
symptoms will be far less than with a spinal cord injury. Furthermore, a
severed peripheral nerve is likely to repair itself, whereas the spinal cord
does not.
Sensory fibers are attached to receptors of various kinds. In
particular, a map of innervation by sensory fibers has been developed on
the surface of the body. Each segment of the spinal cord is responsible,
through its sensory fibers, for supplying a part of the surface of the body.
The skin supplied by the spinal cord segment is referred to as a
dermatome. Dermatomes can be used to determine the extent of spinal
cord injury. A map of the dermatomes is shown in Figure 14.14.
Sample Questions
1. Which of the following is composed of sensory fibers only? a. ventral roots of spinal nerves b. ventral rami of spinal nerves c. dorsal roots of spinal nerves d. dorsal rami of spinal nerves
2. What is the name given to a collection of nerve cell bodies outside the
CNS? a. ganglion b. horn c. tract d. nucleus
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3. How many pairs of cervical spinal nerves are there? a. 5 b. 8 c. 10 d. 12
4. Identify the nerve injured if a patient is unable to move his thumb.
a. ulnar b. median c. axillary d. radial
5. The phenic nerve develops from this plexus.
a. sacral b. lumbar c. brachial d. cervical
Answers to Sample Questions
1. c; 2. a; 3. b; 4. b; 5. d
Written Assignment #5
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Trace a nervous impulse from the spinal cord to the rectus femoris
muscle, noting different nervous tissue structures the impulse will
have to negotiate along the way. (A couple of tips: you will have to
start by looking up, in Chapter 11, the nerve that innervates the
rectus femoris muscle. Start at the anterior gray horn of the spinal
cord; then trace the impulse out the intervertebral foremen and
through the appropriate plexus.)
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2. Define a nerve plexus. List spinal nerves that contribute to the
formation of the four major plexuses. Generally, describe muscle
groups innervated by nerves from each of the plexuses. Identify the
anatomical location where each plexus is found.
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Lesson 15 Autonomic Nervous System
Reading Assignment
Let the objectives guide your reading of Chapter 15 in your
textbook. There is a lot more information in the chapter than you are
required to know, but do make sure to give the chapter at least one
complete reading.
Objectives
By the end of this lesson, you should be able to:
1. Contrast autonomic and somatic systems (see Figure 15.2). Define
anatomical differences between sympathetic and parasympathetic
divisions of the autonomic nervous system (see Table 15.1).
2. Locate ganglia for the ANS: pre-vertebral (peripheral) ganglia,
sympathetic trunk, and terminal ganglia (Figures 15.5 and 15.7).
3. Locate the adrenal medulla (Figure 15.7) and explain its
relationship to the ANS.
4. Describe the possible fates of pre-ganglionic sympathetic axons.
Define white and gray rami communicans (see Figures 15.9–15.13).
5. Know the general effects of sympathetic and parasympathetic
innervation of visceral effectors listed on Table 15.2.
6. List "higher centers" that influence the autonomic nervous system.
7. Describe the role and location of visceral sensory/afferent neurons.
Define referred pain.
Discussion
Much of what you have to accomplish relates to comparing the
autonomic nervous system (ANS) to the somatic system and comparing
the two components of the ANS to one another. We will begin by
comparing the ANS to the somatic system.
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If you recall, the somatic motor system is responsible for
innervation for voluntary muscle (skeletal muscle). By contrast, the ANS is
responsible for innervation of involuntary muscle (smooth and cardiac
muscle). The somatic system is a one neuron system. That is, an axon from
a motor neuron cell body (located in the anterior gray horn of the spinal
cord) travels directly to the muscle it is to innervate before forming a
neuromuscular junction with the muscle cell. The ANS is a two neuron
motor system. The first neuron cell body is located in the central nervous
system. An axon from the first neuron synapses on the second neuron in a
peripheral ganglion; then an axon from the second neuron proceeds to the
muscle to be innervated. Some of these differences are illustrated in Figure
15.2
Another difference between the somatic system and ANS is that the
neurotransmitter substances differ. The transmitter substance for the
somatic system is always acetylcholine (ACh). The transmitter for the ANS
can either be ACh or norepinephrine. Lastly, somatic stimulation is always
excitatory; ANS innervation may lead to excitation or inhibition of the
involuntary muscle.
Now study Figures 15.5 and 15.7 and Table 15.1 for graphic and
verbal summary of the differences between the sympathetic and
parasympathetic divisions of the ANS. Note the following key differences:
1. origin of the preganglionic neurons for each division and 2. location of
the peripheral ganglia for each division. In sum, a pathway within the ANS
will have three components: preganglionic neurons, autonomic ganglia
and postganglionic neurons, and effectors (involuntary muscle).
Part of the adrenal gland, the adrenal medulla, can be included in
the sympathetic division of the ANS. The adrenal medulla secretes
epinephrine (and norepinephrine) into the bloodstream with effects
almost identical to sympathetic stimulation. The widespread activation of
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a sympathetic response is partly attributable to the rapid distribution of
hormones from the adrenal medulla in the bloodstream.
Now let's briefly take a closer look at the location of the ganglia in
each division. Return to Figures 15.5 and 15.7. Note that sympathetic
ganglia lie in one of two places. They are either close to the spinal cord in a
structure called the sympathetic trunk (alongside the vertebral column)
but a few are located peripherally, in front of the vertebral column (and
the CNS). The latter are referred to as pre-vertebral (peripheral) ganglia.
Regardless, sympathetic ganglia are relatively close to the vertebral
column (and the CNS). Examine Figure 15.7 to confirm this point. Notice
that the ganglia for the parasympathetic division (called terminal ganglia)
are almost all situated on or close to the structure to be innervated, quite
distant from the CNS.
We earlier noted that the two divisions employed different
transmitter substances. Specifically, the parasympathetic division uses
only ACh as a transmitter substance. The sympathetic division's
transmitter substance will vary depending on whether the synapse is
between preganglionic axon and postganglionic neuron or between
postganglionic axon and involuntary muscle. In the case of the former, the
transmitter substance is also ACh. But with the second synapse
(neuromuscular junction) the transmitter substance is almost always
norepinephrine. ("Almost" because there are a few exceptions where the
transmitter substance at the sympathetic division's postganglionic
neuron's synapse with the smooth or cardiac muscle is also ACh.) Figure
15.4 summarizes transmitter substance similarities and differences
between the two divisions.
For most organs and viscera, the ANS supplies dual innervation.
That is both sympathetic and parasympathetic divisions innervate
effectors. The result of dual innervation could be antagonistic (opposite) to
one another, complementary, or cooperative.
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Figures 15.9–15.13 illustrate the three possible fates of
preganglionic sympathetic axons. They can do any of the following:
1. Synapse on the sympathetic trunk and be distributed with a spinal
nerve at the same spinal segment;
2. Synapse at a higher or lower level of the sympathetic trunk and be
distributed with a spinal nerve at a different spinal segment; or
3. Pass through the sympathetic trunk and become a splanchnic nerve
to one of the three peripheral ganglia anterior to the vertebral
column (e.g., celiac). See Figure 15.7.
When you are comfortable with the materials we have covered so
far, turn to Table 15.2. Objective five requires you to know the general
effects for the sympathetic and parasympathetic stimulation. If you look
over Table 15.2 a couple of times, you should get the sense that the
sympathetic division usually produces a response in the organ or structure
innervated consistent with meeting an emergency. Conversely, the
parasympathetic division almost always results in a rest and recovery
response in the structure innervated. These general effects are consistent
with the primary purposes of each division. The sympathetic division is
concerned with responses to emergency situations, often called the "fight
or flight response." Energies and resources within the body are mobilized
for action. In contrast, the parasympathetic division seeks to conserve
energy and take care of routine, but necessary, "housekeeping" chores that
must be done for the body to function properly on a day-to-day basis.
Hence, if you think of what you would want the organ to be doing in an
emergency, you will usually be able to deduce the sympathetic effect on the
organ. The parasympathetic effect is generally the opposite, or it has no
effect on the organ or tissue.
Higher control of the ANS is exerted mostly through the
hypothalamus, reticular formation in the brainstem, and control centers in
the medulla oblongata, but several other structures have lesser effects. The
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anterior nucleus of the thalamus and the cerebral cortex can have some
effect on the ANS.
Although the majority of discussion of the ANS features its visceral
motor functions, visceral sensory neurons do exist and it is clear we can
feel some modalities in visceral structures (especially temperature and
pain). However, unlike the clear anatomical differences between visceral
motor neurons, it turns out that visceral sensory neurons are found in the
same location as somatic sensory neurons—in the dorsal root ganglia. One
notable difference between somatic sensory and visceral sensory systems
does exist: the concept of referred pain. Whereas pain associated with
somatic sensory receptors is projected to its actual physical location (e.g.,
pain from a cut finger), with the visceral sensory system it is projected to
an area of the body that does not always correspond to the visceral organ
(e.g., pain associated with a heart attack). (See Figure 15.15.)
Sample Questions
Try these after you believe you have mastered the material covered
in the objectives.
1. Which statement concerning the ANS is not true? a. It usually operates without conscious control. b. It regulates visceral activities. c. All of its axons are afferent (sensory) fibers. d. It contains ganglia.
2. Control of the ANS is exerted by all but which of the following?
a. medulla oblongata b. hypothalamus c. filum terminale d. thalamus
3. Axons from preganglionic neurons of the parasympathetic division of
the ANS synapse here. a. sympathetic chain ganglia b. peripheral ganglia c. terminal ganglia
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d. dorsal root ganglia
4. Which is not part of the fight or flight response? a. dilation of the pupils b. increased heart rate c. constriction of blood vessels in the viscera d. contraction of the urinary bladder
5. Preganglionic fibers of the sympathetic division tend to be shorter than
postganglionic fibers for this reason: a. their ganglia lie closer to the vertebral column. b. they have gray rami communicantes. c. they do not synapse with splanchnic nerves. d. they have to synapse on more postganglionic neurons.
Answers to Sample Questions
1. c; 2. c; 3. c; 4. d; 5. a
Written Assignment #6
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Identify and explain the principle differences between the voluntary
nervous system and autonomic nervous system.
2. Define autonomic ganglion? Describe the location and function of
the three types of autonomic ganglia. Define and discriminate white
and gray rami communicantes.
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Lesson 16 Special Senses
Reading Assignment
Read Caper 16 in your text. Use the objectives below to help identify
important information in the chapter.
Objectives
By the end of this lesson, you should be able to:
1. Contrast general sensory receptors and special sensory receptors.
2. Describe the microscopic anatomy of receptors for taste and smell.
Summarize their neural pathways and the cranial nerves involved.
3. Identify the anatomy of the eye, including lacrimal gland, tunics
(fibrous, vascular, sensory), anterior chamber (glaucoma), posterior
chamber, lens (cataract).
4. Describe the neural pathway for vision: retina, optic nerve, optic
chiasma, optic tract, thalamus, optic radiations, visual cortex.
5. Identify the anatomy of hearing and balance.
! Outer ear—external auditory meatus, tympanic membrane
! Middle ear—ossicles, pharyngotympanic tube
! Inner ear—semicircular ducts, utricle, saccule, cochlear duct,
spiral organ (of Corti), helicotrema
6. Summarize the neural pathways for hearing and balance.
Discussion
Special senses, suchas vision and hearing, distinguish themselves
from general sensory receptors on the basis of two main differences. First
of all, general sensory receptors are spread throughout the body—e.g.,
receptors for touch are found everywhere. In contrast special senses are
resticted to the head region. Secondly, special sense information is
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transported by way of cranial nerves, not spinal nerves, as are most
general senses.
Smell and taste are two special senses that are quite old from the
point of view of evolution—most mammals are able to smell and taste. In
fact, in lower species these two modalities are primary methods through
which the creature understands the environment. Taste and smell are
preserved in the human species, but are not as vital to interpretation of the
environment as with lower species.
Smell receptors are located primarily in the upper nasal mucosa
and nasal septum (the cartilage that separates the two nasal cavities).
Figure 16.3 displays olfactory receptors and the formation of the olfactory
nerve (first cranial nerve) from the convergence of olfactory receptor cell
fibers. The olfactory nerve transmits the smell information to the olfactory
cortex (see Figure 13.23b). Of course, the olfactory nerve and smell
information are involved in the primitive limbic system discussed earlier
in this unit.
In contrast, taste is monitored by three cranial nerves—the facial,
glossopharyngeal, and the vagus (cranial nerves 7, 9 and 10 respectively).
However, all three cranial nerves feed taste information into a common
nucleus (the solitary nucleus) in the medulla (see Figure 16.2). From there
taste information has a mandatory synapse on the thalamus and then is
projected to the gustatory cortex on the inferior part of the post-central
gyrus (see Figure 13.23a). As you can observe in Figure 16.2, taste
receptors are embedded in the tongue and pharynx.
Vision is a sensory modality that would be difficult to do without.
Extra-ocular muscles (see Figure 16.6) allow us to voluntarily direct our
gaze in a variety of directions to take in visual-sensory information about
the environment. The anatomy of the eye is provided in Figure 16.7. The
eye is divided into two distinct areas delineated by the anterior and
posterior chambers. The anterior chamber is filled with a fluid substance,
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the aqueous humor. It is produced and drained on an on-going basis.
(Failure to drain enough aqueous humor from the anterior chamber
results in a build-up of pressure that can damage the eye permanently—
glaucoma). In contrast the posterior chamber is filled with a firmer, gel-
like matrix known as the vitreous humor. It is stable and does not need to
be replaced constantly. The vitreous humor gives a stable form and shape
to the eye.
The interior of the eye is lined with three layers or tunics. An outer
fibrous tunic is composed of the sclera posteriorly and the cornea
anteriorly. The anterior cornea is transparent and allows light to pass
through.
The intermediate tunic likewise has an anterior part (the ciliary
body) and a posterior part (the choroid). A part of the ciliary body, the
ciliary zonule, allows the smooth muscle of the ciliary body to adjust the
concavity/convexity of the lens so that light passing through the opening
(the pupil) will strike the sensory receptor for light in the deep tunic (the
retina) and be detected. It is the diameter of the pupil that automatically
adjusts to illumination by constricting or dilating.
The third tunic of the eye is the retina, containing two layers. One of
the layers of the retina contains sensory receptors for light and is called the
neural layer. Fibers from a variety of different types of sensory cells in the
retina pass posteriorly and converge to form the optic nerve (second
cranial nerve). Figure 16.10c shows the fibers converging on the posterior
pole of the eye to form the optic nerve.
Figure 16.15 illustrates the pathway for light information from the
retina to the visual cortex of the occipital lobe of the cerebral cortex.
Objective four lists the structures of the visual pathway in correct order.
You should remember these structures. A point of clarification about
vision though, because cerebral control is contralateral the left visual field
is seen on the right occipital lobe and vice-versa. Further, since one-half of
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each visual field is seen on each retina, the halves of the visual fields must
unite at some point along the way to the visual cortex. This occurs at a
structure called the optic chiasma, where fibers of the inside halves of the
right and left optic nerves cross to the opposite side (illustrated in Figure
16.14). After the fibers have crossed and the left and right visual fields are
completed, the name of the fibers changes to optic tract (from the previous
optic nerve). Following a synapse on the thalamus (remember that all
information accessing the cerebrum must synapse on the thalamus), visual
information is projected to the visual areas on the occipital lobe by way of
optic radiations, completing the pathway for vision.
The sensory receptors for hearing and balance are situated close to
one another in the inner ear. Therefore, it is not unusual for a person who
has a hearing deficit involving the inner ear to also manifest a balance
problem. This is particularly common among older adults and may add to
the risk of sustaining a serious injury from a fall.
The outer ear (see Figure 16.16) consists of a long canal, the
external auditory meatus that ends internally at the tympanic membrane.
Its role is to transmit auditory sensations, which are vibrations in the air.
These vibratory pulsations cause the tympanic membrane to more back
and forth.
Anchored to the tympanic membrane are three small bones, the
auditory ossicles (see Figure 16.16). Between the ossicles are joints that
move in response to movements of the tympanic membrane. One of the
auditory ossicles (the stapes) rests against the oval window of the inner
ear. A pharyngotympanic (auditory) tube connects the throat (pharynx) to
the middle ear. As an aside, the infections that affect many children as
otitis media (an "ear infection") find origin in the pharynx and travel up
the tube to spread the infection to the middle ear.
The inner ear consists of sensory receptors for hearing and balance.
Those for balance are the utricle, saccule and semicircular ducts (see
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Figures 16.18 and 16.21).The utricle is the receptor for linear movement of
the head (as in flexing and extending/nodding the head "yes"). The saccule
allows us to maintain orientation against gravity—static equilibrium. The
semicircular ducts monitor rotational/angular acceleration of the head (as
in rotating the head, or shaking the head "no"). All of the receptors
function in about the same way (see Figures 16.21, 16.22), where a material
(e.g., otolithic membrane, cupula) lags behind a movement of the head.
Eventually the material moves but with some latency compared to the
movement of the head. Once the material moves, it stimulates receptor
hair cells, and then the fibers of the vestibular part of the eighth cranial
nerve.
The neural pathway for balance does not travel to the cerebrum for
the most part, as with most other sensory modalities. Instead, balance
information travels to vestibular nuclei in the medulla oblongata and the
cerebellum.
Detail of the auditory portion of the inner ear is illustrated in Figure
16.23. But perhaps a better way to understand the cochlea is displayed in
the Figures 16.16, 16.19 and 16.23. The stapes causes vibrations against the
oval window, which in turn causes vibrations in the fluid (perilymph) of
the scali vestibule. The vibrations are further conveyed from the scali
vestibule to the fluid (endolymph) of the cochlear duct. These vibrations
cause the basilar membrane inside the cochlear duct to vibrate,
stimulating receptor hair cells for hearing (for a closer view see Figure
16.19). Once the hair cells bend the cochlear portion of the eighth cranial
nerve is stimulated.
Unlike, balance information, auditory information is conveyed to
the cerebral cortex (primary auditory area on the temporal lobe) after a
synapse on the thalamus. Compared to vision, where all impulses from the
retina on one side travel to the opposite cerebral hemisphere, auditory
information from each ear travels to each hemisphere. This is why a
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person can still hear in both ears even though trauma (e.g., a stroke) may
destroy the primary auditory cortex on one cerebral hemisphere. However,
as mentioned in the lesson on the CNS, damage to language areas on the
dominant hemisphere will result in difficulty using language (aphasia)
even though the person can hear.
Sample Questions
Try these after you believe you have mastered the material covered
in the objectives.
1. Where are sensory receptors for smell located? a. vomer b. nasal mucosa c. palate d. pharynx
2. Which cranial nerve does not carry sensory information for taste?
a. facial b. glossopharyngeal c. trigeminal d. vagus
3. This part of the fibrous tanic of the eye is white, tough, and opaque. a. cornea b. choroid c. sclera d. retina
4. This part of the ears contains the auditory ossicles. a. external b. middle c. internal
5. The stapes transmits vibrations against the oval window of the inner ear, causing this to move. a. utricle b. perilymph c. saccule d. tectarial membrane
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Answers to Sample Questions
1. b; 2. c; 3. c; 4. b; 5. b
Go on to Lesson 17.
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Lesson 17 Endocrine System
Reading Assignment
Read Chapter 25 in your textbook. As always, use the objectives to
key your reading.
Objectives
By the end of this lesson, you should be able to:
1. Define and differentiate exocrine and endocrine glands.
2. Identify and locate the major endocrine glands (see Figure 25.1).
3. Define the three basic types of hormones: steroids, proteins, and
amines.
4. Describe control of hormone secretion by negative feedback
mechanisms and neural control pathways. Also, define the three
mechanisms for control of hormone release (humoral, neural,
hormonal—see Figure 25.2).
5. Generally describe how nervous and endocrine systems interact at
the pituitary gland (hypophysis) and hypothalamus.
6. List the hormones of each of the following endocrine glands and
their general effects: pituitary (hypophysis), thyroid, parathyroids,
adrenals, pancreas, ovaries, testes, and thymus.
7. Describe the etiology of diabetes mellitus (Type I and Type II) and
contrast it with diabetes insipidus.
Discussion
Hormones are blood-borne molecules that travel to certain cells
and cause a physiologic response. Endocrine glands do their work by
secreting hormones that travel in the bloodstream and influence other
cells to perform certain physiological tasks, increase or decrease the speed
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of a certain process or cause other endocrine glands to secrete yet other
hormones. Hormones eventually find their way into the blood stream
where they can move more quickly to their target cells—the cells that
respond to the hormone. The aim of the endocrine system and its
hormones is to maintain homeostasis, all things functioning normally and
in a well-adjusted fashion in the body's internal environment.
Endocrine glands contrast with a second type of gland in several
ways. Exocrine glands never secrete hormones, their products tend to be
substances such as oil, sweat, enzymes, etc. Exocrine gland products are
secreted onto epithelium, tubes, body cavities, or covering and lining
epithelium. For example, sweat is secreted onto the skin, covering
epithelium. Because of this, secretions from one exocrine gland do not
have a widespread effect relative to the hormones of an endocrine gland.
Hormones are distributed widely via the vascular system.
Endocrine glands tend to operate by way of a negative feedback
loop. This means they operate just like the thermostat in your house. If the
temperature falls, the thermostat detects it and turns on the furnace.
When the temperature increases to an acceptable level, the thermostat
causes the furnace to turn off. Decreases in temperature bring about (the
opposite) an increase in the activity of the furnace (and vice versa).
Likewise, presence or absence of certain products or substances in
the blood stream are detected by the endocrine gland, causing hormone
secretion to turn on or off, according to need. In this way, the internal
environment of the body is kept in proper working order—in balance, in
homeostasis. This sort of feedback control is characteristic of humoral
control of hormone release (see Figure 25.2). Besides humoral control,
endocrine glands may be controlled by other (tropic) hormones secreted
by the pituitary gland, or by direct nervous stimulation called hormonal
and neural control respectively (see Figure 25.2).
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Identify the major endocrine glands in Figure 25.1. You should be
able to locate all of the glands and give an anatomical description of where
each is found.
Hormones are of three basic types: steroids, proteins, or amines.
The hormones differ in how each brings about changes in target cells.
Steroid hormones can enter target cells and alter protein synthesis within
the cell.
Protein and amine hormones bind with receptor sites on the target
cell membrane causing changes in the cell membrane, which in turn may
cause changes in a variety of inter-cellular activities.
Perhaps the single most important endocrine gland is the pituitary
(also called the hypophysis, sometimes called the "master" endocrine
gland). It is located in the sella turcica of the sphenoid bone. The pituitary
can actually be thought of as two glands in one, the anterior (also called
the adenohypophysis) and posterior (also called the neurohypophysis)
pituitary glands. The pituitary and hypothalamus represent the meeting of
the nervous system and the endocrine system. This is more than just a
meeting, however, because the hypothalamus can have a great influence
on the pituitary gland. The hypothalamus and the pituitary are portrayed
in Figures 25.3 through 25.5.
The hypothalamus exerts much of its control over the anterior
pituitary (adenohypophysis) through the use of releasing factors.
Releasing factors pass from the hypothalamus to the anterior part of the
pituitary via blood vessels in the infundibulum and cause the anterior
pituitary to secrete its hormones (see Figure 25.4). Some of the pituitary
hormones then act on target cells that are non-specific. That is, growth
hormone stimulates many different cells to grow: bone, muscle, or fat
tissue. In contrast, the anterior pituitary also secretes a series of hormones
that act on still other endocrine glands. The target cells for these hormones
are other glands. The second group of hormones are referred to as tropic
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hormones. For example, thyroid stimulating hormone is a tropic hormone
because it stimulates the thyroid gland. Table 25.1 lists the primary actions
of the hormones of the pituitary. See Figure 25.4 for the relationship
between the anterior pituitary and the hypothalamus.
Turning to the posterior pituitary, (neurohypophysis) we find that it
secretes only two "hormones," oxytocin and antidiuretic hormone (ADH).
Closer inspection of the posterior pituitary (see Figure 25.5) reveals that
axons from the hypothalamus extend through the infundibulum into the
posterior pituitary. As a result, oxytocin and antidiuretic hormone are
actually closer to neurotransmitter substances, manufactured in the
hypothalamus, transported to the posterior pituitary and then secreted
into the bloodstream by the posterior pituitary. The supraoptic nucleus
produces ADH in the hypothalamus, while the paraventricular nucleus
produces oxytocin in the hypothalamus. Both are then secreted by the
neuro-hypophysis.
Study Table 25.1 and remember the major action of each of the
pituitary's hormones. To make your task a little easier, the tropic
hormones usually tell you a lot about where their target cells are. Use this
information to deduce each tropic hormone's effect. Also, for lutenizing
hormone and follicle stimulating hormone, just remember that they are
both involved in development of mature gametes (sperm cells or egg cells),
preparation for fertilization and gestation, and production of sex
hormones (estrogen and testosterone).
The thyroid gland is situated in the neck, anterior to the trachea,
superior to the sternum, and inferior to the larynx (see Figure 25.6). The
thyroid plays a major role in augmenting metabolic activity by controlling
the rate of metabolism. This is accomplished through the secretion of
thyroid hormones. A second hormone secreted by the thyroid is calcitonin.
Along with parathyroid hormone (discussed below), calcitonin regulates
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blood calcium levels. The presence of an adequate level of calcium in the
bloodstream is essential for life.
The parathyroid glands (there are usually four of them) are located
on the posterior surface of the thyroid (see Figure 25.7). Parathyroid
hormone is the only hormone produced and secreted by the parathyroid
gland. You should know how it acts to increase blood calcium: releasing it
from bone, stimulating its absorption in the digestive tract, and retaining
it through the kidneys. (Just for fun: can you remember the tissue we
discussed earlier that serves as a storage area for calcium?)
The adrenal glands sit atop the kidneys (see Figure 25.8); this is
why they are sometimes called the suprarenal glands. The adrenal gland is
a fairly complex structure, with three different zones or levels to its outer
shell (cortex), and a centrally located medulla (center). Each of these four
constituents gives rise to its own hormone. Read about each of these
hormones and their general effects in the textbook. With regard to the
adrenal medulla, some further comment is necessary. If you pay special
attention to the section on the adrenal medulla, you will find that
splanchnic nerves (preganglionic axons) from the sympathetic division of
the ANS innervate the adrenal medulla. Second, you will find that the
hormones secreted by the adrenal medulla produce the same effects as the
sympathetic division of the ANS. It is no coincidence that norepinephrine
is the transmitter substance for postganglionic axons of the sympathetic
division of the ANS and also a hormone secreted by the adrenal medulla.
In a sense you might think of the adrenal medulla as yet another ganglion
that preganglionic fibers from the sympathetic division of the ANS can
synapse on.
The pancreas is involved in the regulation of blood glucose (sugar).
It is pictured in Figures 25.1 and 25.10. It is located posterior to the
stomach and first part of the small intestine, the duodenum. The pancreas
is part exocrine gland, concerned with the secretion of digestive enzymes.
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But its endocrine functions command our attention for the purposes of the
present lesson. It secretes two hormones that produce opposite effects.
Insulin decreases blood glucose, while glucagon increases blood glucose.
Insufficient or absent secretion of insulin results in diabetes mellitus, with
the familiar excess of glucose in the bloodstream and urine.
The ovaries (female) and testes (male) together are referred to as
the gonads. You can locate each of the gonads on the composite Figure
25.1. The gonads secrete what are generally known as sex hormones
(testosterone in the male; estrogen and progesterone in the female). In
general, sex hormones control secondary sex characteristics (placement of
hair, relative amounts of muscle and fat, weight of skeleton, etc.),
stimulate maturation of gametes (egg cells and sperm cells), and promote
activities that support pregnancy.
The thymus gland (see Figure 25.1) is located posterior to the
sternum in the upper center portion of the chest. The thymus gland is not
well understood, but it has been implicated in the body's immune system.
Its major role seems to be production of a specialized white blood cell
known as a T-lymphocyte. Because of its role in the immune system, the
thymus gland and T-lymphocytes are among the most studied tissues in
AIDS research.
Sample Questions
1. This name is given to a hormone that acts on another endocrine gland. a. feedback hormone b. acceleratory hormone c. tropic hormone d. inhibiting hormone
2. Which endocrine gland listed below is most closely related to the
sympathetic division of the ANS? a. pancreas b. adrenal medulla c. parathyroid
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d. thyroid
3. Why is the posterior pituitary not a typical endocrine gland? a. It receives a rich blood supply. b. It does not make its own hormones. c. It is not near the brain. d. It contains ducts.
4. Name the antagonistic hormones that regulate blood calcium.
a. insulin-glucagon b. aldosterone-cortisone c. PTH-calcitonin d. HGH-ADH
5. Hypophysis is another name for this gland.
a. pituitary b. testes c. pancreas d. thyroid
Answers to Sample Questions
1. c; 2. b; 3. b; 4. c; 5. a
Examination #3
Examination #3 follows Lesson 17. This will be a one-hour,
supervised examination. No books, notes, or other aids may be brought to
the exam. The examination consists of forty multiple-choice questions of
the same type you have seen in the sections of sample questions in each
lesson. The exam questions are allocated according to the number of
objectives per topic.
Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
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UNIT 5 VISCERAL SYSTEMS
Lesson 18 Heart
Lesson 19 Blood Vessels and Lymphatics
Written Assignment #7
Lesson 20 Respiratory System
Lesson 21 Digestive System
Written Assignment #8
Lesson 22 Urinary System
Lesson 23 Reproductive System
Examination #4
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Lesson 18 Heart
Reading Assignment
Read Chapter 18 in your textbook pertaining to the heart. You
might be surprised by the relatively few objectives for this important
organ. However, to answer each objective, you will have to know quite a bit
of information.
Objectives
By the end of this lesson, you should be able to:
1. Define the functions of the circulatory system. Also define atrium,
ventricle, systole, diastole, pulmonary circuit, and systemic circuit.
2. Describe the location of the heart in the mediastinum (see Figure
18.2).
3. Identify the structure of the pericardium and heart wall (Figure
18.3).
4. Identify the sulci, chambers, great vessels and valves (and papillary
muscles) of the heart on both anterior, posterior, and internal views
(Figure 18.5).
5. Trace the course of a erythrocyte through the heart and lungs,
beginning at the right atrium and ending at the aorta. Define
structural and functional differences between the left and right
heart.
6. Identify the origin of the heart beat and the intrinsic conduction
system of the heart (Figure 18.14). Identify the effects of
sympathetic and parasympathetic stimulation of the heart (Figure
18.15).
7. Identify the major vessels of coronary circulation (Figure 18.16) and
the general areas each supplies or drains.
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8. Identify major risk factor for cardio-vascular disease. Define a
congestive heart failure, angina pectoris, ischemia, myocardial
infarction, incompetent valve, stenotic valve, and heart block.
Discussion
The circulatory system includes fluids, solid elements, tubes, and a
pump.
The circulatory system functions to transport gases and nutrients as
well as waste products. It carries hormones to target cells rapidly. And
because of the white blood cells (leukocytes) and platelets (essential for
clotting) in the blood, the circulatory system plays important roles in
defense of the body (immune response, clotting).
Blood is comprised of liquid (plasma) and solids (formed elements).
The formed elements are mostly cells that perform different roles within
the vascular system, though some of the cells may leave the blood stream
to do their job. The formed elements of blood usually compose about forty-
five percent of the total blood volume. This percentage is known as a
hematocrit.
The heart is located in the mediastinum, medial to each lung,
anterior to the vertebral column, posterior to the sternum. It is slightly off
center, to the left. The heart lies somewhat on its right side. It terminates
inferiorly in an apex (point) that is directed downward and to the left.
Notice that the four chambers of the heart, atria (2) and ventricles (2), are
not of equal size or presence. For example, most of the right ventricle is
seen in an anterior view of the heart (Figure 18.5b), but the largest
chamber, the left ventricle, makes up most of the left, inferior/posterior
surface of the heart (Figure 18.5d). Note also that most of the "great
vessels" enter or exit the heart at its superior border. Identify the aorta,
pulmonary trunk, superior vena cava, and inferior vena cava.
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The heart is surrounded by a triple-layered membrane, including
fibrous pericardium (see Figure 18.3). A space between the parietal and
visceral layers of the serous pericardium contains the pericardial fluid,
which serves as a lubricant and reduces friction as the heart beats. Hence,
the pericardial sac protects and stabilizes the heart in the mediastinum.
The wall of the heart is made up of an outer layer of epicardium.
Note that the epicardium is the same as the visceral layer of the serous
pericardium (see Figure 18.3). This is obviously not muscle, in contrast to
the second layer of the heart wall. The myocardium comprises the great
majority of the thickness of the heart wall, especially the ventricles. As you
might expect, it is comprised of cardiac muscle. Finally, there is an inner
layer of epithelium (known as endocardium) and connective tissue (elastic
and collagen fibers) that line the inner aspect of the heart's chambers.
The heart is a four-chambered pump (Figure 18.5e). The two upper
chambers are called atria (left and right atrium). There are walls (septa)
inside the heart dividing the atria from one another and the ventricles
from one another (interatrial and interventricular septa respectively).
However, the right atrium communicates with the right ventricle and the
left atrium communicates with the left ventricle. Each side of the heart
works as a unit (see Figure 18.6). The right (atrium and ventricle) side is
the pulmonary circuit (because it pumps blood to the lungs) and the left
side is the systemic circuit (because it pumps blood to the remaining
systems, e.g., digestive). Study Figure 18.5 to confirm the anterior,
posterior, and internal presentation of each chamber.
Also refer to Figures 18.5b and 18.5d to identify grooves on the
external surface of the heart, called sulci. One sulcus divides atria from
ventricles, the coronary sulcus. Another pair of grooves divides the
ventricles on the anterior and posterior surface of the heart, the anterior
and posterior interventricular sulci respectively. These landmarks are
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important to know because they divide the chambers of the heart and help
with identification of coronary blood vessels (covered below).
As we noted earlier, the atria communicate with the ventricles. They
do this through atrioventricular valves. The major valves of the heart are
shown in Figures 18.9 and 18.10. There are two atrioventricular valves, a
tricuspid valve on the right and a bicuspid/mitral valve on the left. Once
blood is pumped from atria into ventricles on each side, the tricuspid and
mitral valves prevent regurgitation of blood from the ventricles back into
the atria when the ventricles contract. Note, papillary muscles in the walls
of the ventricles attach to the valves by way of tendons, (chordae tendinae)
to help the valves resist the back flow of blood from ventricles into atria,
shown in Figures 18.5e and 18.9.
Notice a second set of valves in Figures 18.5e and 18.10. These
valves protect the opening between the right ventricle and pulmonary
artery and the opening between the left ventricle and the aorta. They are
collectively known as semilunar valves (pulmonary semilunar on the right;
aortic semilunar on the left). You should pay attention to the differences
between atrioventricular valves and semilunar valves. One major
difference is that the former have papillary muscles attached to them; the
latter do not.
The heart beat is said to be intrinsic; that is, it arises from a
structure located inside the heart itself. This structure is called the
"pacemaker," or more properly, the sinoatrial (SA) node. This node, along
with the others illustrated in Figure 18.14, cause the heart to beat. Study
the path of the bundles of fibers. They pass down the septum (wall)
separating the left and right ventricles and then swing lateral onto the
outer surfaces of each ventricle. This pattern suggests that the atria
contract from the top down, driving blood into the ventricles; whereas, the
ventricles contract from the bottom up, driving blood upward into the
pulmonary trunk (right ventricle) or the aorta (left ventricle). The
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autonomic nervous system (ANS) does innervate the heart (Figure 18.15)
and can cause it to increase rate and strength of contraction (sympathetic
effect) or decrease rate of contraction (parasympathetic effect).
ANS stimulation of the heart is controlled by "centers" in the
medulla (remember them when we talked about the brainstem?). There is
one center (cardioacceleratory) that will increase the rate and the strength
of the heart's contractions through the sympathetic division of the ANS.
Cardiac (sympathetic) nerves derived from upper thoracic levels of the
spinal cord stimulate the heart rate to increase and contract more
forcefully. A cardioinhibitory center has the opposite effect, slowing the
heart rate and decreasing the strength of contraction. Parasympathetic
(inhibitory) effects are produced primarily by way of innervation of the
heart by the vagus nerve (tenth cranial nerve).
As you already know, the heart is a muscle. All muscles need oxygen
and nutrients supplied via the bloodstream to do their work properly, so it
should come as no surprise to you that the heart receives a blood supply.
Coronary circulation (see Figure 18.16) begins with blood ejected from the
first part of the aorta (the ascending aorta) into the left and right coronary
arteries. The left coronary then gives off two major branches, a circumflex
and an anterior interventricular (between the ventricles). Likewise, the
right coronary has two branches, a marginal and posterior ventricular (see
Figure 18.16).
As a rule, coronary arteries supply any adjacent chamber or any
chamber they touch. For example, the anterior interventricular artery
supplies blood to two chambers it is adjacent to—the left and right
ventricles.
Once oxygen is depleted and blood in coronary circulation is ready
to return to the right atrium, it does so through the major venous channels
illustrated in Figure 18.16. The pattern is somewhat simpler for venous
return from coronary circulation than for arterial distribution. A great
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cardiac vein drains the anterior portion of the heart, a middle cardiac vein
drains the posterior aspect of the heart, and a small cardiac vein drains the
inferior-right portion of the heart. All three empty into the coronary sinus,
which in turn empties into the right atrium.
The basic pattern of heart action is as follows: the right heart
receives venous blood into the right atrium, pumps it into the right
ventricle where it is next pumped into the pulmonary trunk and arteries to
be passed on to the lungs. Oxygen is loaded onto red blood cells and
carbon dioxide removed in the lungs. The oxygenated blood returns to the
left atrium via pulmonary veins, then to left ventricle. Finally, the powerful
left ventricle drives oxygenated blood into the aorta for distribution
throughout the body (major circulatory routes will be discussed in the next
lesson). Note that while we have separated the pulmonary and systemic
parts of the heart's work, both are working concurrently. That is, blood is
being pumped through the pulmonary (right) side of the heart at the same
time different blood is being pumped through the systemic (left) side of
the heart.
Research and longitudinal studies of mortality in Western culture
point to heart disease and specifically heart attacks as one of the leading
causes of death. While some people are more predisposed to heart attacks
than others, it is mostly lifestyle risk factors that account for manifestation
of a heart attack: excess weight, hypertension (high blood pressure),
excessive saturated fats in the diet, smoking, diabetes mellitus, and lack of
regular exercise are the leading modifiable risk factors.
Look up the definitions for the remaining terms in objective
number 8 throughout the chapter.
Sample Questions
1. This atrioventricular valve is on the same side of the heart as the origin of the aorta.
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a. aortic semilunar b. tricuspid c. mitral d. pulmonary semilunar
2. Which chamber of the heart has the thickest walls?
a. right ventricle b. left ventricle c. right atrium d. left atrium
3. Which great vessel of the heart is associated with the right ventricle?
a. superior vena cava b. inferior vena cava c. aorta d. pulmonary trunk
4. Which of the following is not part of the heart wall?
a. pericardium b. epicardium c. endocardium d. myocardium
5. This vein empties de-oxygenated blood from coronary circulation into
the right atrium. a. great cardiac vein b. small cardiac vein c. middle cardiac vein d. coronary sinus
Answers to Sample Questions
1. c; 2. b; 3. d; 4. a; 5. d
Go on to Lesson 19.
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Lesson 19 Blood Vessels and Lymphatics
Reading Assignment
Read Chapters 19 and 20 pertaining to the second part of our study
of the cardiovascular system, the blood vessels. As always, use the
objectives listed below to guide your reading.
Objectives
By the end of this lesson, you should be able to:
1. Describe the typical blood vessel in cross-section (see Figure 19.1).
Contrast the structure and function of elastic arteries, muscular
arteries, capillaries, and veins.
2. Discuss the problem of venous return to the heart. Identify the
relative allocation of blood volume in veins compared to arteries.
3. Identify principal arteries (see Figure 19.8) and veins (Figure
19.18):
a. Arteries: arch of the aorta and its major branches (Figure
19.9), arteries of the head and neck (Figure 19.10), arteries of
the upper extremity (Figure 19.11), major branches of the
abdominal aorta (Figure 19.12), and arteries of the lower
extremity (Figure 19.16). Skip branches of the thoracic aorta
and arteries of the pelvic region. See Figure 19.17 for a
summary.
b. Veins: veins draining the head and neck (Figure 19.20), veins
of the upper extremity (Figure 19.21), inferior vena cava and
azygos system (Figure 19.21) of veins of the thorax and
abdominal cavity (Figure 19.23), veins of the lower extremity
(Figure 19.25), and cerebral sinus drainage of the cranium
(Figure 19.20).
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4. Trace the circulation of a red blood cell from left femoral vein to left
femoral artery.
5. Trace the route of blood involved in hepatic portal circulation and
explain its importance (Figure 19.24).
6. State the functions of the lymphatic system.
7. List and define the components of the lymphatic system: lymph,
lymph capillaries (Figure 20.2), lymphatics (lymphatic collecting
vessels), lymph ducts, lymph nodes, spleen, thymus, and tonsils.
8. Describe the structure of a typical lymph node (Figures 20.4).
Identify the stroma and parenchyma of a lymph node.
9. Identify the thoracic duct, right lymphatic duct, and cisterna chyli
(Figure 20.3). Describe the general pattern of distribution of lymph
nodes in the body (Figure 20.3).
10. Describe, in general, the plan of lymph circulation from lymphatics
to the thoracic duct and right lymphatic duct to the subclavian veins
(see Figures 20.1 and 20.3).
11. Clinical applications: swollen lymph nodes, edema, monocucleosis,
Hodgkin's disease, AIDS.
Discussion
Just as a heart is likened to a pump, we can characterize the
vascular system as a vast network of tubes that deliver blood to various
destinations. The basic components of this tube system include: arteries,
which carry blood away from the heart; capillaries, which exchange
substances with tissues through their one-cell thick walls; and veins, which
convey blood back to the heart.
A closer look at arteries, capillaries, and veins in Figure 19.1 reveals
several marked structural differences throughout the tube system. A
typical artery has three layers: the first composed of epithelium (called
endothelium) and elastic tissue, the second composed of elastin and
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smooth muscle, and the third composed of elastic and collagenous
connective tissue. These layers are referred to respectively as tunica
intima, tunica media, and tunica externa. Two subtypes of arteries can be
derived from this basic three-layered arrangement, based upon the relative
amounts of connective tissue (especially elastic fibers) and smooth muscle.
The largest arteries lie close to the heart and are placed under the
greatest amount of stress because of the force of blood ejected by the left
ventricle. These large (elastic) arteries, in effect, "catch" the blood and
then recoil to propel the blood further along the arterial network. Large
arteries tend to have less smooth muscle.
Muscular or distributing arteries have considerably more smooth
muscle, though they are somewhat smaller than large elastic arteries. They
provide the greatest resistance to blood flow and are most influential in
determining blood pressure.
Capillaries are composed of a single layer of endothelium (Figure
19.1). This rather obviously makes it easier for substances to move into and
out of the capillary networks throughout the body. Capillaries unite to
form small, two-layered veins called venules so that blood may begin its
trip back to the heart.
Like arteries, veins have three tunics with names identical to those
of arteries. If you study Figure 19.1 and compare arteries and veins, you
will find that the walls of veins are thinner. This is attributable to less
smooth muscle and less elastic tissue in veins. The thin walls of veins are
consistent with the fact that there is far less force being exerted on the
veins. Blood pressure has dropped significantly by the time the blood has
traveled through the maze of arteries and the capillary bed to reach the
venous system. The thinner walls of the veins represent an adaptation to
the lower blood pressure and force behind the blood. Blood pools ("backs
up") in the venous system as a result.
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However, this presents a problem, particularly in the lower
appendages because blood must move toward the heart against gravity.
Part of the solution to this problem can be seen in Figure 19.6. Many veins
are outfitted with one-way valves, which resist the backflow of blood away
from the heart. As you can also see in Figure 19.6, skeletal muscle activity
exerts force on the "column" of blood in the vein and pushes it toward the
heart. The valves in veins assure that the blood will not lose the ground it
has gained, so to speak, and yield to the force of gravity.
Another part of the solution is that the venous system can
accommodate more blood than the arterial system because there are more
veins than arteries. There are both superficial and deep veins, whereas
there are only deep arteries.
Furthermore, the latter fact allows the venous system to
accommodate greater blood volume (about 65 percent) than the arterial
system.
Your textbook goes on to detail the main circulatory routes in the
body. You should have a general knowledge of the tissues that various
circulatory routes lead to. Try to approach the task of learning the selected
arteries and veins with a couple of things in mind. First, remember to test
yourself by photocopying the figures you need to learn, clipping off the
labels, and then trying to label the diagrams yourself. Second, realize that
blood vessels are frequently renamed as they move from one section of the
body to the next. Remember, you may have several names for the same
tube, depending on the part of the body you are talking about.
Begin with the aorta and its major branches shown in Figure 19.9.
Note that the aorta is divided into four sections: ascending, arch, thoracic,
and abdominal. Recognize the two coronary arteries are the first branches
off the (ascending) aorta. You do not have to know the small branches of
the thoracic aorta. But you should know the major branches of the
abdominal aorta (Figure 19.12). The celiac trunk and its branches supply
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the liver, spleen, stomach, and the first part of the small intestine. The
superior mesenteric sends arterial blood to most of (the remainder of) the
small intestines and proximal one-half of the large intestines. The inferior
mesenteric supplies blood to the distal one-half of the large intestines,
sigmoid colon, and rectum. Other branches are named for the organ
supplied—renals supply the kidneys, suprarenals supply the adrenal
glands, and gonadals supply ovaries or testes.
When you feel pretty confident about the arm (Figure 19.11), move
on to the lower extremity, illustrated in Figure 19.16. The abdominal aorta
ends by forming the common iliac arteries at the level of L-4 vertebra. The
common iliacs give a branch to supply the pelvic contents (the internal
iliac artery) and continue as the external iliac arteries on each side. Once
the external iliac passes into the lower extremities (under the inguinal
ligament), it is called the femoral artery. Try to label an unlabeled copy of
the same figure. Concentrate on the femoral, poplitial, anterior and
posterior tibial, fibular (peroneal) arteries. Also, identify dorsal pedis and
lateral and medial plantar arteries.
The arteries of the head and neck are pictured in Figure 19.9.
Arteries of the head and neck are branches off the external carotid and
pretty much tell you the tissue supplied in the name of the artery (e.g.,
facial artery supplies most structures of the face). The internal carotid and
vertebral arteries supply blood to the brain. This complex of arteries forms
a sort of circle—the cerebral arterial circle (Circle of Willis), responsible for
blood supply to the brain.
Most of the deep veins take on names identical to those of the
arteries they customarily parallel. Study Figure 19.18 and note the major
veins. We can pretty much assume that you know the general pattern of
venous return to the heart if you have learned the arteries well. Take note
of the following exceptions: jugulars instead of carotids; inferior and
superior vena cavae instead of aorta; basilic, brachial, and cephalic instead
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of only a brachial; the femoral is fed by the popliteal and supplemented by
the great saphenous. The common iliacs join to form the inferior vena
cava, subclavians become brachiocephalics on each side (there is only one
brachiocephalic artery/trunk), and the superior vena cava is formed from
the joining of the right and left brachiocephalics.
The veins of the head and neck parallel the arteries serving the head
and neck, except for the jugulars noted above. As for venous drainage of
the brain, the internal jugular is fed by cranial venous sinuses (see Figure
19.20). Look at Figure 19.20 to obtain a sense of the distribution of the
cranial venous sinuses seen through the transparent skull. Note that the
cerebral sinuses are made up of the dura mater layer of the meninges.
The azygos system of veins supplements the inferior cava in
draining the anterior body cavity (Figure 19.21). Most of the intercostal
veins drain into the azygos systems. Note that the azygos system assists
the inferior vena cava but empties into the superior vena cava.
The upper extremity is drained by veins that pretty much parallel
the arteries supplying the upper extremity, with the exceptions noted
above. Venous arches drain into radial and ulnar veins, which in turn feed
into the brachial vein. Cephalic and basilic veins are superficial in the arm
and supplement the brachial. You should also note the median cubital vein
in the cubital fossa of the elbow (Figure 19.21). It connects with the basilic
vein medially.
Like the upper extremity, the lower extremity has veins that pretty
much parallel the course taken by arterial supply (Figure 19.26). The
major superficial veins of the lower extremity are the great and small
saphenous veins, which empty into the femoral vein in the thigh and the
popliteal vein at the knee respectively.
Veins of the abdominal cavity (Figure 19.23) are almost identical to
the arterial supply to the different organs (e.g., renal vein drains the
kidney).
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Part of Written Assignment number 7 requires that you trace the
course of red blood cells (RBC) from one location to another. It would be
impossible for me to review all of the possible routes of circulation with
you. Therefore, instead of reviewing particular circulation patterns, I will
give you the following rules to follow:
1. Whenever you route an RBC from venous to arterial, the RBC must
pass through the heart.
2. Try to learn the major blood vessels before you attempt to trace an
RBC.
3. Veins move blood toward the heart; arteries move blood away from
the heart.
4. Many times the name of the "tube" (blood vessel) changes with a
change in location, but it still is the same "tube."
A significant variation in the venous system in the anterior body
cavity is the hepatic portal system (Figures 19.24, 19.25). The hepatic
portal system is a series of veins that coalesce to form the hepatic portal
vein (its two main tributaries are the splenic and the superior mesenteric
vein, though several other veins also contribute). Ultimately, venous blood
from the stomach, pancreas, and small and large intestine reaches the liver
for the purposes of filtration and processing of the nutrient rich blood
from the digestive system. The blood is eventually returned to general
venous circulation through the hepatic veins on the posterior surface of
the liver emptying into the inferior vena cava.
The lymphatic system's main task is to drain excess fluid from
tissue spaces. The lymphatic system then transports this fluid, called
lymph, back toward the heart through lymphatic vessels. To do this job,
the lymphatic system includes the following components: lymph, lymph
vessels, lymph nodes, and the spleen, tonsils, and thymus gland.
Besides its role in returning the fluid lymph to the venous system,
near the heart (we will talk about the general plan of lymph circulation
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below), the lymphatic system also plays a major role in the body's immune
defense system by producing some white blood cells (lymphocytes) and
antibodies. The lymphatic system also transports fats from the digestive
tract to the blood and returns blood proteins back to the vascular system.
The lymphatic system begins as a series of lymph capillaries that
are more permeable than capillaries of the vascular system (Figure
20.2). This stands to reason because a major task of the lymphatic system
is to absorb excess intercellular fluid. Once the intercellular fluid enters
the lymph capillary, it is called lymph.
Lymph capillaries begin to aggregate and form larger vessels called
lymphatics (lymphatic collecting vessels). Lymphatic collecting vessels are
comparable to veins, but differ from them in that they have more valves,
thinner walls, and pass through lymph nodes. Lymphatic collecting vessels
generally follow blood vessels and converge on two major channels (the
thoracic duct and the right lymphatic duct) that return the lymph to the
bloodstream (Figure 20.3).
The thoracic duct drains all but the right extremity, thorax, and
head (Figure 20.3), which is drained by the right lymphatic duct. The
cisterna chyli lies in the abdomen near the origin of the thoracic duct. It
collects lymph from the lower extremities and drains into the thoracic
duct. The thoracic duct and right lymphatic duct return lymph to the blood
stream by emptying at the junctions of subclavian and internal jugular
veins.
Lymph nodes resemble a lima bean in shape. Figure 20.4 shows a
typical lymph node. Nodes are placed throughout the length of the
lymphatic channels (see nodes in Figure 20.3 for examples). Lymph
channels carrying lymph into the node are called afferent lymphatic
vessels and those channeling lymph out of the node are called efferent
lymphatic vessels. As you can observe on our prototypical node (Figure
20.4) the afferent vessels enter the convex surface of the node, whereas the
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efferent vessels exit on the concave side of the node at an indentation
called the hilus. Identify the following structures on the node diagrammed
in Figure 20.4: hilus, capsule, and trabeculae.
Lymphocytes are produced in lymph follicles/nodules of the node
(Figure 20.4). They are the white blood cells that produce the antibodies
which will attack foreign, disease-carrying cells that invade the body.
Phagocytic cells, which ingest and destroy debris and foreign molecules,
are also found in the lymph node. Nodes essentially filter the lymph to
remove any waste products, debris, or foreign substances.
The functional part of a lymph node is called the parenchyma,
found in the medulla and cortex of the node. Figure 20.4 shows the
stroma, the structural part of the node, which includes the capsule and
trabeculae.
The general pattern of lymph circulation (see Figure 20.1) begins in
the spaces between cells, called intercellular spaces. Fluid from the
intercellular space moves into lymphatic capillaries, where it is called
lymph. Lymph capillaries merge to become lymphatics (lymphatic
collecting vessels). The lymph then encounters several nodes. Eventually,
the lymph will find its way to either the thoracic duct or the right
lymphatic duct. These ducts return the lymph into the venous system at
the junction of the internal jugular and subclavian veins.
There are three larger, specialized lymph organs you should locate—
tonsils, spleen, and thymus gland. The tonsils are situated in the posterior
wall of the pharynx (i.e., the throat). They function as large lymph nodes.
The spleen (Figure 20.10) is the largest lymphoid tissue located
posterior to the stomach and under the diaphragm. It is buried deep
within the abdominal cavity. The spleen, however, filters blood, not lymph.
It performs tasks similar to those of a lymph node: ingesting foreign
invaders and worn out materials, producing lymphocytes and the added
task of storing blood (for emergency situations).
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The thymus gland (see Figure 20.10) is located posterior to the
upper section of the sternum, extending somewhat into the lower reaches
of the neck. The thymus helps T-lymphocytes develop.
You should be able to identify areas on the body where clusters of
lymph nodes can be found (see Figure 20.3). The most palpable nodes are
used in clinical assessment and include the following: cervical, axillary,
and inguinal.
There are several clinical applications for you to look up and define.
I encourage you to read over the section on immunity, but I only want you
to be able to define the clinical applications. For instance, AIDS is a virus
that infects and destroys a helper T-lymphocyte, normally responsible for
directing the immune response of other lymphocytes. This leads to an
increasing susceptibility to infections and related disorders. Look up the
clinical terms on your own.
Sample Questions
1. An obstruction in the inferior vena cava would hamper the return of blood from this area. a. head b. neck c. upper extremities d. lower extremities
2. In hepatic portal circulation, blood eventually returns to the inferior
vena cava through these vessels. a. superior mesenteric veins b. portal veins c. renal veins d. hepatic veins
3. Afferent lymphatic vessels enter a lymph node at this site.
a. hilus b. concave side c. convex side d. medulla
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4. The greatest proportion of elastin is found in which type of vessel? a. large arteries b. capillaries c. medium-sized arteries d. veins
5. Lymph is eventually returned here.
a. venous system b. interstitial fluid reservoir c. arterial system d. spleen (for storage)
Answers to Sample Questions
1. d; 2. d; 3. c; 4. a; 5. a
Written Assignment #7
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Describe the course of a red blood cell from the right brachial vein
to the right ulnar artery.
2. Trace lymph fluid from inguinal lymph nodes to the venous system,
noting important anatomical structures along the way.
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Lesson 20 Respiratory System
Reading Assignment
Read Chapter 21, "Respiratory System." By now you know to use the
objectives to guide your reading (so, why did I tell you, huh?).
Objectives
By the end of this lesson, you should be able to:
1. List the functions of the respiratory system. Also, define the three
components of respiration.
2. Identify the anatomical structures of the respiratory system (Figure
21.1). Also, name the bones in which paranasal sinuses are found.
3. Identify the following structures of the larynx (Figure 21.3b, 21.5):
thyroid cartilage, cricoid cartilage, glottis, epiglottis, hyoid bone
and trachea.
4. Describe the structure of an alveolus (Figure 21.3b and 21.10).
5. Identify the lobes, fissures, hilus, "root," and cardiac notch of the
right and left lungs (Figure 21.13). Also, distinguish the left from the
right lung. Identify and describe the pleurae. Summarize tissue
changes in the respiratory system from nasal cavity to alveoli.
6. Describe the mechanics of breathing and the muscles involved. See
Figure 21.16.
7. Identify structures involved in the nervous control of breathing
(ventilation) (Figures 21.17, 21.18).
8. Clinical applications, define each of the following: cystic fibrosis,
pneumothorax, lung cancer, RDS, asthma, and emphysema.
Discussion
The organs of the respiratory system are diagrammed in Figure
21.1. They include the nasal cavity, pharynx, larynx, trachea, bronchi, and
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lungs. Like most of the internal body systems (like the digestive, vascular,
urinary), the respiratory system is largely a network of tubes running to
and from organs pivotal in maintaining the integrity of the system, in this
case—the lungs. The difference between the respiratory system and other
tube networks is that it transports gases rather than solids or fluids.
As your books states, respiration consists of three related functions:
ventilation, external respiration, and internal respiration. External
respiration consists of gas exchange between the external environment
and the red blood cells within the capillaries of the lungs. Internal
respiration has more to do with the distribution of gases, the exchange of
gases between the vascular system and the tissues it supplies. Ventilation
is synonymous with breathing.
But the respiratory system is involved in other functions. These
include voice production and protective reflexes. The respiratory system
adds "character" to sound and makes it into language. The respiratory
system also has some built-in reflexes that protect it—the forceful
expulsion of air in a sneeze represents the respiratory system's effort to
dislodge dust and debris from the nasal cavity or upper reaches of the
respiratory system.
The respiratory system also includes the paranasal sinuses. These
cavities in the frontal, ethmoid, sphenoid, and maxillary bones reduce the
weight of the skull. The sinuses function to moisten and filter inspired air.
The diagram of the upper portions of the respiratory system is
important (Figure 21.3b). It includes the nasal cavity which descends into
what we might consider the "throat" in lay terms. The throat (pharynx) is
actually composed of several important structures that are involved in
both the respiratory and digestive systems. The respiratory components
include the pharynx, larynx, and trachea. The larynx is actually
represented by the thyroid cartilage and the cricoid cartilage (Figure 21.5).
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The larynx merges inferiorly into the trachea. The trachea is composed of
16 to 20 C-shaped cartilages which are open posteriorly (Figure 21.7).
The inside of the larynx is composed of an opening called the
glottis. The glottis is protected superiorly by a flap of elastic cartilage
called the epiglottis. It allows food to pass over the glottis to the esophagus
without entering the glottis and becoming lodged in the trachea. The
lumen (opening) of the glottis can be increased or decreased in size by
contraction and relaxation of the true vocal cords. These are illustrated in
Figure 21.6 along with the false vocal cords.
Note that the nature of the epithelium changes as one moves from
the nasal cavity inferiorly. While the nasal cavity and nasopharyx are
comprised of pseudostratified epithelium, the oropharynx and
laryngopharynx consist of stratified epithelium. Once in the trachea,
however, the epithelium reverts back to the pseudostratified type.
Structures involved in external respiration are represented in a
respiratory zone (Figure 21.9). The respiratory zone begins with a terminal
bronchiole that becomes progressively smaller (respiratory bronchiole,
alveolar duct, aveolar sac) and ends with individual aveoli.
Gases are exchanged across two membranes, one vascular
(capillary), one respiratory (aveolus). Figure 21.10 displays these two
membranes. You already know that capillaries are made up of a single-
layered, endothelial cell membrane. Alveoli are composed of a wall of
simple squamous epithelium (type I alveolar cells). Type II alveolar cells
(septal cells) produce surfactant, a lubricant important in ventilation.
Phagocytic cells (alveolar macrophages) are also found in the walls of
alveoli and function as phagocytic cells anywhere else—they destroy
foreign material.
The thin walled structure of both the alveolus and the capillary
allow for an easy exchange of gases (oxygen and carbon dioxide) between
the respiratory and vascular systems. Gases diffuse (go from areas of high
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to low concentration) across the alveolar-capillary membrane. Carbon
dioxide diffuses into the lungs, for subsequent expiration, and oxygen
diffuses into the blood stream, for subsequent distribution to body tissues.
The lungs are divided into two or three lobes depending on the right
or left. On the right lung, horizontal and oblique fissures mark off
superior, middle, and inferior lobes. On the left lung, a single oblique
fissure separates superior and inferior lobes (Figure 21.13). The left lung
also is marked on its medial surface with a cardiac notch made by the
heart as it lies in the mediastinum. Also identify the hilus and "root" of
each lung.
Lobes of each lung can be broken down even further into lobules.
Terminal bronchioles are separated into discrete compartments bordered
by (elastic) connective tissue. The respiratory bronchioles (Figure 21.9)
within the lobule continue to divide into smaller units called alveolar
ducts. It is within the latter structure that alveoli arise, the functional units
of gas exchange in the lungs.
The tubes leading to the alveoli become progressively smaller.
Other than knowing the main/primary bronchi, you do not have to know
the names of progressively smaller bronchi. However, you should know
how the tissue composition of the tubes changes as the tubes become
smaller. Besides changes in epithelium noted above, from trachea to
bronchioles, one finds progressively less cartilage (the larynx and trachea
are primarily cartilage) and more smooth muscle (the smooth muscles of
the bronchioles is primarily responsible for constriction and dilation of the
airways).
The lungs dominate the thoracic cavity, except for the mediastinum.
Each lung is contained within a double-walled protective sac, called the
pleura. The outer layer is the parietal pleura and the inner layer is the
visceral pleura. The space between the visceral pleura and the parietal
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pleura is called the pleural cavity. The pleural cavity contains a thin layer
of fluid to reduce friction between the two layers of pleurae (Figure 21.11).
Breathing is the mechanical part of respiration involving taking air
into the lungs and then expiring it. It is properly called pulmonary
ventilation (Figure 21.16) and can be broken into two parts: inspiration
and expiration.
Inspiration is an active process involving the expenditure of energy
and the use of several muscle groups. Inspiration is accomplished by
creating a favorable pressure gradient for air to flow into the lungs. This is
done by making the pressure inside the thoracic cavity less than that of the
air outside of the lungs. To make the pressure inside the thoracic cavity
less, the thoracic cavity must be enlarged, and this is accomplished by
increasing the superior-posterior dimensions of the cavity (by contraction
of the diaphragm) and increasing the anterior-posterior dimensions of the
thoracic cavity (by contraction of the external intercostals). The scalene
muscles and the sternocleidomastoid also assist in respiration during
stressful activity or forced inspiration.
Expiration is a more passive process, primarily attributable to the
recoil of the elastic tissue within the stroma of the lungs and the relaxation
of the muscles responsible for inspiration. Forceful expiration is
accomplished by the contraction of the abdominal muscles and the
internal intercostals.
Having already covered the brain, you can probably guess that
nervous control of respiration is controlled by a "center" in the medulla
oblongata of the brainstem. As it turns out, the medullary rhythmicity area
sets the basic respiratory rate. However, several other neurological
structures are involved too. Pneumotaxic and apneustic areas in the pons
help coordinate or modify the relationship between inspiration and
expiration. Finally, we all know from experience that we voluntarily
modify our breathing patterns (holding breath, forcible expiration, etc.).
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Hence, the cerebral cortex is also involved in neurological control of
respiration.
Chemoreceptors in the carotid and aortic bodies send sensory
information to respiratory centers in the brainstem via the
glossopharyngial and vagus nerves (see Figures 21.17 and 21.18). This
allows for moment-to-moment correction of ventilation and respiration.
On your own, look up the clinical applications in objective number
8. You should be able to define each term.
Sample Questions
1. This name is given to the exchange of gases between the lungs and blood. a. inspiration b. expiration c. internal respiration d. external respiration
2. What is the total number of lobes in both lungs?
a. 6 b. 5 c. 4 d. 2
3. Which of the following is not a part of the respiratory system?
a. nose b. eustachian/auditory tube c. pharynx d. larynx
4. Which of the following would not be found in an alveolus of the lung?
a. macrophages b. simple epithelium c. Type II aveolar cells d. plasma cells
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5. Which of the following areas of the brain helps control respiration? a. cerebellum b. hypothalamus c. midbrain d. pons
Answers to Sample Questions
1. d; 2. b; 3. b; 4. d; 5. d
Go on to Lesson 21.
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Lesson 21 Digestive System
Reading Assignment
Read Chapter 22 in your textbook.
Objectives
1. Name the primary functions of the digestive system. Identify the
major organs and tubes associated with digestion (Figure 22.1).
2. Identify and define the peritoneum, mesentery, mesocolon,
falciform ligament, lesser omentum, and greater omentum (Figure
22.10).
3. Describe the general histology (Figure 22.5) of the GI tract: mucosa,
submucosa, muscularis, and serosa.
4. Identify the structures of the upper part of the digestive system
(Figure 22.12): oral cavity, tongue, palate, oropharynxs, and
esophagus. Also name and identify the three major salivary glands
(Figure 22.16).
5. Describe internal and external anatomy of the stomach and its
major functions (Figure 22.18).
6. Identify the different parts of the small (Figures 22.1 and 22.21) and
large intestines (Figures 22.1 and 22.22). State the primary
functions of the small and large intestines.
7. Identify and locate the organs of the digestive system and accessory
organs of digestion: liver, gallbladder, pancreas (Figures 22.26,
22.20). Generally describe the digestive functions of the liver,
gallbladder, and pancreas.
Discussion
The obvious functions of the digestive system all relate to activities
designed to facilitate the absorption of nutrients, water, and trace minerals
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through the lining of the digestive tract, especially the small and large
intestines. Digestion actually refers to the mechanical and chemical
breakdown of food, which is a pre-requisite to absorption.
The major organs of the digestive system are illustrated in Figure
22.1. I will be summarizing the major anatomical and functional features
of each of the organs and tubes in Figure 22.1 throughout this lesson.
We have already observed that the heart and lungs are enveloped in
protective layers of epithelial and connective tissue. The same holds for
some of the components of the digestive system. The general term used to
refer to these protective and stabilizing membranes is peritoneum. The
parietal peritoneum lines the inner surfaces of the abdominal cavity and
the visceral peritoneum actually touches the organ/structure (Figure
22.9).
The peritoneum can be further divided into sub-units depending on
placement and organ it is associated with. As the parietal peritoneum
extends anteriorly from the dorsal wall of the abdomen, it forms a double-
layered membrane which envelopes most of the organs of the abdominal
cavity. Depending on the organ, the double-layered membrane of
peritoneum may suspend the organ from the posterior wall of the
abdomino-pelvic cavity (see Figure 22.9). If it suspends the small
intestine, then it is called the mesentery. If it suspends a part of the large
intestine, then it is called the mesocolon (Figure 22.10). In sum, the
mesentery and the mesocolon serve to suspend the intestines from the
posterior abdominal wall, leaving the intestines enough latitude for
movement, but keeping them stabilized through attachment to the
posterior abdominal wall.
Several other parts of the double-layered part of the peritoneum are
also illustrated in Figure 22.10. These structures include: the falciform
ligament, which supports the liver anteriorly, the lesser omentum, which
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suspends the stomach from the liver, and the greater omentum, which
loosely attaches the lower portion of the stomach to the transverse colon.
The peritoneal covering continues around the organs of the
digestive system, where it is known as the visceral peritoneum (Figure
22.9). This is in keeping with the convention we have observed for the
heart and the lungs already (e.g., the visceral pleura covers the lungs).
A typical cross-section through the digestive tract reveals that it is a
multi-layered organ with specialized tissues at each layer (Figure 22.5).
The innermost layer is called the mucosa. It is composed of epithelium, as
you probably guessed. It is the portion of the digestive tract responsible for
absorptive functions. The mucosa also contains a thin layer of smooth
muscle called the muscularis mucosa. (Do not confuse this with the
muscularis layer described below. This thin layer of smooth muscle is
actually included in the mucosa layer.)
The second layer is called the submucosa (see Figure 22.5); it is
composed of loose connective tissue which is highly vascular. The
submucosa is very important to the process of absorption of nutrients, as it
contains many blood vessels and lymphatic channels which pass close to
the surface of the lumen of the digestive tract.
The third layer of the digestive tract is the muscularis layer (see
Figure 22.5). It is specialized to churn and mix food. It may also contract
in a manner that will move food further down the digestive tract
(segmentation, peristalsis).
The fourth layer of the typical segment of the digestive tract is
known as the serosa (see Figure 22.5). It is a membrane of epithelial cells
covering loose connective tissue.
In the superior reaches of the digestive system one can observe
several structures in common with the respiratory system (Figure 22.12).
The two systems share a common passageway for a brief period, the
portion of the pharynx posterior to the oral cavity. The mouth, tongue, and
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the palate are included in the digestive system but not the respiratory
because air enters through the nasal cavity, superior to the palate. The
respiratory and digestive systems diverge from one another at the inferior
portion of the pharynx, where the larynx is positioned anteriorly and the
esophagus is positioned posteriorly. As previously mentioned in the
respiratory lesson, the epiglottis covers over the glottis (the opening to the
larynx) so that food may pass over the air passage instead of being inspired
into the trachea or lungs.
You should study Figure 22.16 next. Identify the three major
salivary glands and the general location of each. The salivary glands
secrete digestive enzymes to initiate the process of breaking down the
food.
After food passes down the esophagus it enters the stomach (Figure
22.18). It is here that the digestive process continues in earnest, although
little in the way of absorption occurs in the stomach. Instead, the stomach
secretes a number of digestive enzymes, (e.g., pepsin) that transform the
food into a state more suitable to absorption. By the time the food has
been processed by the stomach it is called chyme. Make certain to identify
by landmarks on the internal and external stomach
The stomach is a J-shaped organ. The concave portion is called the
lesser curvature and the convex inferior part of the "J" is the greater
curvature. These represent the attachments of lesser and greater omentum
respectively. The most superior part of the stomach is called the fundus,
while the superior part in the area of the esophagus is called the cardia.
The area of the stomach near the first part of the small intestines is known
as the pylorus. Note, the folded inner surface of the stomach known as the
rugae.
The majority of nutrient and water absorption is the job of the small
and large intestines. The small intestine absorbs most of the food, and the
large intestine absorbs most of the water and minerals.
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The small intestine is composed of the three parts (Figure 22.1). In
order from the stomach to the large intestine, one would encounter the
duodenum (the first ten inches), the jejunum (the next three feet), and the
ileum (the remaining six-seven feet). The ileum ends at the ileocecal valve
which leads into the cecum of the large intestine. Together, the three parts
of the small intestine receive digestive secretions from the liver, pancreas,
and gall bladder, continue the breakdown of the chyme, and absorb
nutrients.
The large intestine or colon (Figure 22.22) consists of several parts
as well. The large intestine begins as the cecum, a pouch at the inferior
extent of the ascending colon. This is a short segment of the large
intestine; the appendix is a blind pouch that is suspended form the cecum.
Absorption of nutrients ends in the small intestines, but the large
intestines still has the important job of absorbing water and minerals.
Extending in a superior direction from the cecum is the ascending
colon. It turns medially at the hepatic flexure and becomes the transverse
colon. The transverse colon runs across the anterior body wall and then
turns inferiorly at the splenic flexure to become the descending colon.
From this point the colon ends in three short segments: a short sigmoid
colon, the rectum, and the anal canal (Figure 22.22).
Other features to note on Figure 22.22 include the haustra,
dilations in the large intestine throughout its course. The haustra are
periodic dilations where the contents of the large intestine pause for
further mixing and absorption of water and minerals. The large intestine is
also covered with a longitudinal muscle throughout its entire length called
the taeniae coli. The taeniae coli are capable of strong peristaltic
contractions that move the contents of the large intestine along toward the
rectum for defecation.
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Assisting in the digestion and absorption of food are three accessory
organs: the liver, gall bladder, and pancreas. All three secrete enzymes that
assist in digestion.
The liver is situated in the superior right portion of the abdominal
cavity (Figures 22.21, 22.26), just inferior to the diaphragm. The liver has
four lobes; left, right, caudate, and quadrate. The latter two are seen only
on an inferior view. The liver is attached to the anterior body wall by the
falciform ligament.
From our earlier discussion of hepatic portal circulation you know
that the liver plays an important role in the filtration of blood from the
intestines. Indeed, important functions of the liver include the removal of
old erythrocytes, filtration of bacteria and toxins, and storage of glucose in
the form of glycogen.
From the point of view of digestion, however, the essential function
of the liver is production of bile. Bile is needed in the breakdown and
absorption of fats in the digestive tract. The liver produces bile that is
stored in the gall bladder (Figure 22.26). When bile is to be secreted into
the duodenum, the gall bladder secretes bile into the cystic duct and the
liver secretes bile into the common hepatic duct. These two structures join
to form the common bile duct to the duodenum (Figure 22.20).
The last of the accessory digestive organs is the pancreas (see
Figure 22.20). You may recall that the pancreas is an endocrine gland. In
fact, it has both endocrine and exocrine functions. The latter are
associated with the digestive system. Like the liver and the gall bladder,
the pancreas has a duct that leads to the first part of the small intestine
(Figure 22.20). The pancreas secretes pancreatic juice into the pancreatic
duct. The pancreatic duct joins with the common bile duct at the
duodenum to form the hepatopancreatic ampulla (Figure 22.20). The
pancreatic juice contains enzymes that assist in the digestion of
carbohydrates, fats, and proteins.
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Sample Questions
1. Name the portion of the peritoneum that suspends parts of the large intestines from the posterior wall of the abdominal cavity. a. mesocolon b. mesentery c. lesser omentum d. retroperitoneum
2. This part of the small intestine would be cut first if surgery was being
performed to remove an obstruction from the duodenum. a. mucosa b. muscularis c. serosa d. submucosa
3. This part of the digestive system is shared with the respiratory system.
a. larynx b. pharynx c. palate d. submandibular gland
4. This structure is the first that would be encountered by a button
swallowed by a child after the button passed through the ileum. a. cecum b. hepatic flexure c. ascending colon d. jejunum
5. The lesser omentum connects the liver to which of the structures listed
below? a. stomach b. pancreas c. spleen d. gall bladder
Answers to Sample Questions
1. a; 2. c; 3. b; 4. a; 5. a
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Written Assignment #8
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Trace a button swallowed by a child through the digestive system,
noting anatomical structures it would pass through from oral cavity
to anus.
2. Three major accessory digestive organs contribute digestive
enzymes to the process by way of the hepatopancreatic ampulla.
Identify the three organs and their enzymes. Also explain how
enzymes from each organ reach the hepatopancreatic ampulla.
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Lesson 22 Urinary System
Reading Assignment
Read Chapter 23 on the urinary system. Pay attention to the
objectives for the lesson.
Objectives
1. Identify the organs of the urinary system (Figure 23.1). Also, state
the functions of the urinary system.
2. Describe the external (location, hilus) and internal anatomy of the
kidneys: cortex, medulla, renal pyramids, minor calyx, major calyx,
and renal pelvis (Figure 23.3).
3. Define the microscopic anatomy of a nephron: glomerulus,
glomerular capsule, tubules, loop of Henle, vasa reta, peritubular
capillaries, collecting tubule, and papillary duct (Figures 23.4 and
23.5).
4. Describe the basic functions of each part of a nephron: filtration,
reabsorption, secretion.
5. Name the tissue layers of the ureters and the urinary bladder, (also
identify detrusor muscle, rugae).
6. Identify the urethra (and sphinctors) and the bladder trigone
(Figure 23.16).
7. Describe the normal micturation and identify the nervous control of
micturation: visceral afferent neurons, micturation center (pons),
parasympathetic, sympathetic, and somatic pathways (see Figure
23.17).
8. Trace a voided molecule of water from kidney to urethra.
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Discussion
Like the digestive and respiratory systems earlier, the urinary
system is a network of tubes connecting various organs. It also transports
fluid like the vascular system. But as you can see by Figure 23.1 the urinary
system is a lot more simple and quite a bit shorter than the digestive
system.
The kidneys drain into two tubes on either side of the abdominal
cavity. These tubes are called ureters. The ureters drain into the urinary
bladder, which in turn drains urine into the urethra to be voided from the
body. The components of the urinary system are identified in Figure 23.1.
The primary functions of the urinary system are to filter blood for
toxins and waste products, and to secrete excess water. The kidneys help
maintain the balance of electrolytes and the amount of water in the body
at suitable levels.
The kidneys are located against the posterior abdominal wall
between T12 and L3 vertebrae and the beginning of the lumbar vertebrae.
They are also retroperitoneal (posterior to the peritoneal membranes).
Normally, people have two kidneys, but it is not unusual to have only one
kidney.
Though larger, the kidneys are shaped similar to the lymph nodes,
somewhat like a lima bean. The concave surface has a hilus, like the lymph
node. Similarities end there, however, because the kidneys are responsible
for filtering blood not lymph.
Figure 23.3 reveals the gross appearance of the kidney. It has a
peripherally located cortex surrounding an inner medullary area. Tubes
are plentiful throughout. The minor calyces then unite to form the major
calyx. Major calyces converge at the renal pelvis and hilus of each kidney.
Ureters begin at the hilus of each kidney.
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The histology of the kidney is represented by the basic functional
unit called the nephron. A nephron is illustrated in Figures 23.4, 23.5, and
23.9. A network of capillaries, the glomerulus (Figure 23.6), filters blood
and permits the filtrate of water and waste products to enter the proximal
part of the nephron. Most of the water is reabsorbed from the nephron's
tubules back into the vascular system through capillaries surrounding the
tubules of the nephron (Figure 23.9).
The tubule leading from the nephron does not lead directly to the
collecting duct of the nephron, but rather the tubule is tortuous (winding)
and include a lengthy, convoluted section proximally, a nephron loop, and
a lengthy, distal convoluted tubule (Figure 23.5). From the collecting duct
of each individual nephron, the urine passes into the medulla of the kidney
where it is received by the minor calyx (when it can be properly called
urine) and then on to the major calyx and into the ureter.
The nephron works through three processes—filtration,
reabsorption, and secretion. Filtration occurs at the glomerulus, while
reabsorption and secretion occur in the tubules.
The ureter and the bladder are similar to the other tube systems
inside the body in the sense that each is comprised of several layers of
tissue. The general theme of the tubes within the body has been epithelium
on the inside, smooth muscle in the middle, and connective tissue on the
outside.
The ureter has an inner layer of mucosa which is comprised of
transitional epithelium. Transitional epithelium allows for considerable
distension. A middle smooth muscle layer called muscularis is likewise
found lining the ureters. Finally, an outer layer of fibrous connective
tissue, called the adventitia, completes the walls of the ureters.
The urinary bladder (see Figure 23.16) is similarly organized, with a
layer of transitional epithelium lining the inside of the bladder to permit
distention with the accumulation of urine. The second layer of the bladder
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is the smooth muscle layer, again called the muscularis (also known as the
bladder detrusor muscle). Finally, the most superficial layer of the bladder
is a continuation of the peritoneum called the adventitia.
The inferior opening in the bladder is called the urethra. It is in
close proximity to the openings of each ureter into the bladder and forms a
triangle (Figure 23.16). This area is known as the bladder trigone. Once the
urine has entered the urethra, it must pass internal and extrenal
sphincters to be expelled.
Micturation (urination) is a complex activity (see Figure 23.17) that
is part involuntary and part voluntary. Sympathetic innervation of the
smooth muscle (detrusor muscle) of the urinary bladder allows for filling.
As the bladder fills with urine, stretch receptors in the detrusor muscle of
the bladder are stimulated. This information is feedback to the spinal cord
and then upward to micturation center in the pons. The micturation center
in the pons then causes parasympathetic fibers to stimulate contraction of
the detursor muscle and relaxation of the internal sphinctor. The
micturation center inhibits somatic motor neurons innervating the
external sphinctor. Finally, sympathetic innervation of the bladder is
inhibited to allow for contraction. The cerebrum may also delay urination
for a time by somatic motor stimulation of the external sphinctor.
I will leave you to your own devices to satisfy the final objective of
tracing a water molecule from the kidney to the urethra. Make certain to
detail the pathway followed by the water as it negotiates the complexities
of the nephron. Refer to Figures 23.1, 23.3, 23.5, 23.14 and 23.16 to
develop a complete answer.
Sample Questions
1. Blood is filtered by this structure in the nephron. a. proximal convoluted tubule b. loop of Henle c. glomerulus
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d. collecting duct
2. Name the tube that leads from the kidney to the bladder. a. ureter b. collecting duct c. convoluted tubule d. minor calyx
3. Which of the following is not a component of the urinary system?
a. bladder b. prostate gland c. urethra d. ureter
4. Urine passing through the ureter is in direct contact with which tunic
layer? a. muscularis b. mucosa c. submucosa d. serosa
5. As a water molecule leaves the collecting duct of the nephron, it next
enters this structure. a. ureter b. urethra c. bladder d. minor calyx
Answers to Sample Questions
1. c; 2. a; 3. b; 4. b; 5. d
Go on to Lesson 23.
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Lesson 23 Reproductive System
Reading Assignment
Read Chapter 24 in the textbook. Use the objectives below to guide
your reading.
Objectives
1. List the functions of the reproductive system.
2. Identify and describe structures of the male reproductive system
(Figures 24.1, 24.3): seminiferous tubules, epididymis, ductus (vas)
deferens (and ampulla), seminal vesicle, ejaculatory duct, prostate
gland, bulbourethral gland, urethra, penis.
3. Identify and describe structures of the female reproductive system
(Figures 24.11 and 24.12): ovaries, uterine (fallopian) tube, uterus
(fundus, body, cervix), vagina.
4. Describe the structure and position of the uterus (Figure 24.11).
5. Describe the path taken by a sperm cell from the testes to the
urethra (Figures 24.1, 24.8).
6. Describe the placenta, its anatomy, and the process of exchange
that occurs there (Figure 24.24). Identify substances that may cross
the placenta to the fetus during gestation. Define the terms chorion,
chorionic villi, and decidua basalis.
7. Define the following clinical applications: ovarian cancer, breast
cancer, prostate cancer, testicular cancer.
Discussion
The rather obvious function of the reproductive system is
procreation. Union of a sperm cell and an egg cell is called fertilization and
results in the formation of the zygote, a fertilized egg. The zygote
differentiates as it travels medially down the uterine tube toward the
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uterus for eventual implantation and gestation. (Consult Lesson 2,
"Embryology," and Chapter 3 for a review of the development of the zygote
and its derivatives.) The sex glands accomplish this task through the
production of gametes (sex cells, sperm cells and egg cells).
Besides the rather obvious function, the reproductive systems exert
a significant influence on the development and maintenance of some
tissues—mostly the placement of hair, structure of the larynx, relative
amount of muscle mass, weight of bones, and other features that
distinguish men and women. This is accomplished through the secretion
of sex hormones, testosterone in the male, estrogen and progesterone in
the female. Furthermore, the adequate secretion of sex hormones from the
gonads (sex glands) serves to promote the development of gametes (sex
cells).
Figure 24.1 displays the majority of the structures of the male
reproductive system. This system begins with the structure in the testes
responsible for production of sperm cells, the seminiferous tubules.
Hence, the seminiferous tubules are the functional structures within the
testes. The testes are situated external to the body wall in a sack known as
the scrotum. The scrotum can constrict to bring the testes closer to the
body for warmth. But normally the testes are suspended in the relaxed
scrotum because sperm requires a somewhat lower temperature than core
body temperature to be produced. Sperm should not be confused with the
fluid it is suspended in, semen. Semen is produced by separate structures
in the male reproductive system (see below).
A structure closely associated with a testis is the epididymis,
positioned on the posterior surface of a testis. The epididymis functions to
store and nourish immature sperm cells deposited there from the
seminiferous tubules (see Figure 24.1).
The ductus deferens is a long tube leading from the epididymis to
the ejaculatory duct (see Figure 24.1). The ductus deferens takes a long
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and tortuous route, at one point arching over the urinary bladder and
ureter before coursing posterior to the urinary bladder. The transition
from the ductus deferens to the ejaculatory duct is signaled by its merger
with a duct from the seminal vesicle.
After transporting the sperm to the vicinity of the seminal vesicle
(Figure 24.1) the ductus deferens joins a short duct from the seminal
vesicle to form the ejaculatory duct. It is at this point that some semen is
added to the sperm from the seminal vesicle. The seminal vesicle
contributes about 60 percent of the total volume of semen.
Most of the remaining semen is added by the very next accessory
gland, the prostate gland (see Figures 24.1 and 24.8). Semen from the
prostate gland is added as the ejaculatory duct passes through the gland
and joins the male urethra.
Figure 24.8 also illustrates the bulbourethral glands. The glands are
responsible for producing a viscous lubricant for the urethra at the time of
coitus. Note that the secretions of the bulbourethral glands are not part of
the semen.
The final part of the trip for the sperm cell suspended in the semen
is through a tube the reproductive system shares with the urinary system—
the urethra. The sympathetic and parasympathetic divisions of the ANS
cooperate to stimulate different aspects of the sexual excitation and the
outcome of coitus for the male—ejaculation.
The female reproductive system includes the ovaries, uterine tube,
uterus (womb), and the vagina. These structures are pictured in Figure
24.10. Although the female reproductive system's physiology is
complicated compared to that of the male, its anatomy is rather
straightforward.
The ovaries are situated laterally against the inside margin of the
pelvis, the iliac fossa (Figure 24.12). The ovary on each side is the
equivalent of the testes in the male and is responsible for the production of
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the female reproductive cell, the egg cell. The female is born with all the
egg cells she will ever have. The egg cells are not produced anew with each
cycle, but rather dormant/immature cells mature and are released in a
predetermined order. Once the activated egg cell is ready, it is released by
the ovary—the act of ovulation.
Once the egg cell has ovulated it travels, surprisingly, into the
peritoneal cavity in the vicinity of the ovary. It is the job of the uterine tube
and its appendages (the fimbrae) to capture the egg cell from the
peritoneal cavity and help it begin its trip medially toward the uterus.
Normally, union of the sperm cell and egg cell (fertilization) occurs in the
distal 1/3rd of the uterine tube. The zygote then travels toward the uterus
while experiencing rapid cell division to form a ball of cells referred to as a
morula (see Lesson 2 on Embryology).
Once the morula enters the centrally positioned uterus, it
differentiates into a structure called a blastocyst. This is the structure that
implants itself into the inner layer of the uterus (see Figure 24.12), the
endometrium. The endometrium of the uterus is an optimal environment
in which the blastocyst may thrive, developing and differentiating into the
embryo and then the fetus. The gross appearance of the uterus is that of an
upside-down triangle, with its apex pointing in an inferior direction. The
inferior neck-like region of the uterus is called the cervix. The cervix is a
vital landmark during the birth process. Much of the labor during the birth
process amounts to dilation of the cervix to the size of 10 centimeters so
that the infant's head can pass through the birth canal. The superior, top
region of the uterus is known as the fundus (note the fundus of the
stomach in comparison). The lateral sides of the uterus make up most of
the body of the organ.
The birth canal is the vagina (see Figure 24.12). The vagina serves
as the female sex organ during coitus and the birth canal during delivery of
the infant. At the time of birth, the infant is moved (head first in a normal
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delivery) down the birth canal after it separates from the wall of the
uterus.
In addition to the delivery of the infant, a second structure is
delivered at the time of birth, a temporary organ called the placenta (see
Figure 24.24). The placenta is made up of both fetal and maternal
contributions. The fetal contribution is known as the chorion. The chorion
is comprised of mesoderm cells and a part of the support tissues of the
blastocyst, the trophoblast. The maternal contribution is part of the wall of
the uterine wall (endometrium), the deciduas basalis.
Extensions/projections from the chorion penetrate into the endometrium
to bring fetal blood vessels into close proximity with maternal blood; these
projections of the chorion are known as the chorionic villi.
In a normal pregnancy, fetal and maternal blood do not mix within
the placenta. Rather, fetal blood percolates through capillaries in close
proximity to maternal blood (see Figure 24.24), close enough for the
exchange of oxygen and nutrients for carbon dioxide and waste products
between the mom and the fetus. Unfortunately, other harmful products
may also cross at the placenta, nicotine, alcohol and other drugs, and
viruses. Hence, it is very important that the pregnant woman avoid
substances that would be harmful to the growing infant and monitor diet
and exercise carefully. She is literally eating, drinking, and breathing for
the infant in the womb.
The final pages of Chapter 24 provide a description of each of the
clinical conditions mentioned in the final objective for this lesson. Refer to
those pages and look up each of the cancers listed in objective number 7.
Sample Questions
1. Name the structure in the female reproductive system located posterior and superior to the urinary bladder. a. uterine tube b. uterus
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c. deciduas d. vagina
2. This is a structure that helps form the placenta.
a. cervix b. deciduas basalis c. fundus d. rugae
3. This structure of the male reproductive system is responsible for
temporary storage of sperm cells until they reach maturity. a. epidiymis b. seminiferous tubules c. prostate gland d. bulbourethral gland
4. In the male, this tube is shared by the urinary system and the
reproductive system. a. ureter b. prostate gland c. urethra d. ductus deferens
5. These finger-like projections penetrate the endometrium of the uterus
to bring fetal blood close to maternal blood. a. ciliated tubules b. decidua capsularis c. pseudo-stratified epithelia d. chorionic villi
Answers to Sample Questions
1. b; 2. b; 3. a; 4. c; 5. d
Examination #4 (FINAL)
The final examination follows Lesson 23. This will be a one-hour,
supervised examination in which no books, notes, or other aids may be
brought to the exam. The final consists of forty multiple-choice questions.
Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
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Examination Request Form located at the back of this Study Guide (print
version only).
Course Evaluation
At the end of the semester you will receive an email inviting you to
submit a Course Evaluation. We would greatly appreciate it if you would
take a few moments to complete the Course Evaluation. Your evaluation
and additional written comments will help us improve the Distance
Education courses we offer.
Students who complete their GIS course in two semesters will
receive the email invitation at the end of the second semester.
Transcript
http://registrar.uiowa.edu/transcripts/ Your final course grade will be entered on your permanent student
record at The University of Iowa. Official transcripts are available from the
Office of the Registrar, and may be ordered through ISIS
http://isis.uiowa.edu/ or by phone: call (319).335.0230 or toll free
(800)272-6430 and ask to be transferred.
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