CHAPTER Ihomepages.wmich.edu/~stasko/sppa205/unit1notes.doc · Web viewPathologic anatomy/pathology: Concerned with the effect of disease on anatomical structure. These may include

SPPA 2050 Speech Anatomy and Physiology

What is Anatomy and Physiology? A Brief Introduction

This course focuses on the integrated study of descriptive anatomy and physiology associated with normal speech production. The term descriptive means that you will use words and pictures to acquire and represent your knowledge of the body. Anatomy refers to the study of the structure of organisms and the relation of their parts. Our general notion about anatomy, derived largely from television programs such as CSI and ER, is that it involves the dissection and description of body parts. However, anatomy is a vast discipline that includes large things like bones and very small things like cells and cell organelles. Within the domain of anatomy, there are a number of specializations. A few examples include

Systemic anatomy: Considers the body as a composition of a number of distinct systems, each with relatively homogeneous tissue and/or function.

Regional/topographical anatomy: Considers the relations between structures that are within a region of the body. For example, the head may be studied as a whole even though it contains portions of a number of body systems.

Clinical/applied anatomy: Concerned with the study of anatomy that has relevance for practical sciences such as medicine, surgery, or speech pathology.

Radiologic anatomy: The study of anatomy revealed through imaging techniques. Imaging techniques allow the investigation of non-visible parts without harming or killing the organism. However, different techniques will reveal different body parts with varying levels of resolution. Examples of imaging technology include magnetic resonance

imaging (MRI), computerized tomography (CT), and positron emission tomography (PET).

Microscopic anatomy: Concerned with the structure that cannot be seen with the naked eye (in contrast to gross anatomy). This will include the study of cells and their parts (cytology) and the study of body tissue (histology). As the name implies, this involves the use of microscopes of various types (e.g. light, polarized light, electron etc).

Developmental anatomy/e mbryology: Deals with the growth and development of an organism.

Pathologic anatomy/ pathology: Concerned with the effect of disease on anatomical structure. These may include gross or microscopic changes.

Comparative anatomy: The study of structure across more than one species. For example, we might compare the tongue of the human with the tongue of the frog.

Anthropological anatomy: The anatomical study of persons in history or across race and ethnicity.

Our anatomical investigations over the semester will delve into many of these areas.

Physiology usually refers to the functioning of living organisms or their parts. Physiology, like anatomy, is also a broad discipline, which includes specializations. For example, one could study the physiology of small structures such as the cell or its components (cellular physiology), larger bodily systems (e.g. neurophysiology, respiratory physiology) or how disease influences function (pathophysiology).

Why study Anatomy and Physiology Together? A Brief Rationale

Often, we study anatomy and physiology together because we want to understand why people (and their bodies) operate, behave, and react the way they do. In a discipline like Communicative Disorders, where clinicians deal daily with speech,

language, and hearing behaviors that are disordered in some way. A creed underlying clinical practice is that disordered behaviors can be remediated, moved closer to some state of order. A related, natural assumption is that all behaviors ordered or


not, take some part of their root in the structure of the object that generates them. After all, we say that machines that do a good job at what they are supposed to do – cars that run well or lawnmowers that really cut the grass – are well-designed and well-built. Thus, we can argue that we study anatomy because we want to understand how, when, and to what degree we can “move” behaviors from some disordered, undesirable state, to some ordered state, more easily tolerated by clients and their communities.

In general, when we integrate the study of the structure of things, and their operation, we usually try to work out some “map” between their form and function. We borrow the idea of a map from mathematics, and use the term to refer to some relational statement that links form and function, in the best of all worlds, in some cause-and-effect way. The fundamental value of such mapping statements can be illustrated by the hypothetical example that follows.

We can use lengths of tubing to produce sounds. You can create a sound by slapping the palm of your hand against the end of a piece of steel tubing whose length is a good deal greater than its diameter. The tube acts as a resonator for the sound your hand produces. The tube amplifies a tone whose pitch (i.e., perceived frequency) depends upon the geometry of the cavity inside the resonator. The geometry formed by a uniform piece

of tubing is easy to describe, using only two features. The cavity has a length L, and a cross-sectional area A. L and A completely describe the “anatomy” of the resonating cavity. For convenience, we can use the symbol F to represent the pitch of the tone created by the tube. Thus, F is a variable that describes the resonator’s function. After a little experimentation, it is easy enough to establish that F depends upon, and is inversely proportional to L, but is independent of A (as long as L is significantly bigger than A). When the tube is long (and L is a high number), the pitch of its tone is low (and F is a low number). Conversely, when the tube is short, the pitch of its tone is high. This is a handy fact to know about the relationship between the structure (L and A) and the function (F) of the tube. Now, all of this information may be fine if you plan to assemble a Steel Tube Marching Band, but what does this have to do with Anatomy, Physiology, and Communicative Disorders? This is a concrete example of how, by generating a simple map between form and function, we can take a rational approach to altering the function of these simple tubes. Similarly, we study speech anatomy and physiology, together, because we hope to understand maps that might exist between how people are built, and how they behave. These maps may be used to provide rational bases for therapeutic intervention when (speech) behaviors are not what we, or our clients, would like. If that’s not motivation, I don’t know what is.

Terminology and Reference Frames: Knowing Up from Down, Front from Back, In from Out, etc.

Your gross anatomical obligations in SPPA 2050 are basically of two types. On the one hand, you have an obligation to learn the classical names of body parts (e.g., umbilicus for belly button; clavicle for collar bone; gluteus maximus for what’s often beneath the seat of your pants). You might consider this the “French” part of anatomy. You have to learn -- by memorizing! -- new, correct names (e.g., in French, chat and chapeau) for many things for which you may already have familiar names (e.g., English cat and hat). Of course, we learn French so

that we can communicate with the French when necessary. We learn anatomical terminology so that we can communicate with other health and allied-health professionals. There is no way to avoid the French part of anatomy. This is simply a burden you are obligated to bear.

On the second (anatomical) hand, you also have an obligation, to describe the “geography” of the body. In effect, this obligation boils down to describing where body parts, and parts of parts, are with


respect to one another. Thus, your anatomical education will involve a second important vocabulary, in addition to the classical lexicon for body parts. This second vocabulary includes a simple set of terms that convey direction, and some rules of thumb that allow you to interpret these direction terms.

Establishing a frame of reference suitable for anatomical geography is a more interesting problem than you might imagine, largely because certain choices have to be made, and defended. At least one feature of the necessary frame of reference is determined by the object we want to describe. The body is three-dimensional, and thus, the frame of reference we use to describe its geography must also be three-dimensional. Two familiar three-dimensional reference-frame options are possible. One of these is a spherical coordinate system, in which the position of any object is defined in terms of a distance from some central point of origin, and two angles of inclination or deflection. (A spherical coordinate system is merely an “extended” version of the more familiar two-dimensional polar coordinate system we sometimes use to define the location of one place on the locally flat Earth with respect to some other place). In simple polar terms, we might easily say that South Haven, MI is about 36 miles due west of Kalamazoo. This type of statement is easy and familiar to make and understand. An alternative and possibly more familiar three-dimensional frame of reference is the ever popular Cartesian coordinate system in which the position of any object is defined in terms of three displacements from some point of origin, along mutually orthogonal axes. (A three-dimensional Cartesian system is merely an “extended” version of the familiar two-dimensional Cartesian system we often use to describe where a library might be with respect to the neighborhood gas station (e.g., 2 blocks south, and 3 blocks west.)

Two facts (?) suggest that a Cartesian system might be preferable in anatomy. In general, people seem to be mentally more “at home” with Cartesian than spherical systems. Moreover, a spherical system

demands a specific well-defined center point, from which all distances are measured. It is hard to imagine what point or object in the body might serve that role. The origin that is also necessary for a Cartesian system is less troublesome to define.

We now take on the chore of building up a three-dimensional Cartesian frame of reference to be used in our studies. It is important that we place the frame of reference locally in the body, using body parts to define its axes. This is because we want the axes of the frame of reference to stay with the body as it moves about in space. In local body terms, it is important that up is always the same up. The location of the diaphragm should always be the same with respect to the lungs, whether the body is standing, lying, or on its head. We insure that this will be so, as long as we establish a local, body-based frame of reference. Described below are three orthogonal planes that you will become very, very familiar with over the next few months. Note the body position of the poor soul who is cut up into various pieces by these planes. He is in what we call the anatomical position, standing upright, face forward, arms to the sides, with the palms of the hands forward and thus parallel to the face.

The first plane, known as the mid-sagittal plane, cuts the body into (ideally symmetric) right (dextral) and left (sinistral) halves. Since any plane can be defined by any three non-collinear points, we can locate the mid-sagittal plane in the body by two points defining the “line” that corresponds to the mid-sagittal suture, joining the right and left parietal bones of the calvaria. We can then designate our third “point” to be in the vicinity of any of those landmarks in the middle of the body of which there is only one: e.g., the diastema (a fancy word for gap) between the frontmost of the maxillary teeth; the “tip” of the xyphoid process at the lower margin of the sternum; the symphysis between the pubic bones belonging to the right and left halves of the pelvis; the lower-most “tip” of coccyx. The plane containing the line of the sagittal suture, and any or all of these mid-line “points” is the mid-sagittal plane. All planes parallel to the mid-sagittal plane


are also sagittal planes, though there can be only one mid-sagittal plane.Our second plane must be perpendicular to the mid-sagittal plane, and might be placed to cut the body roughly into front (ventral or anterior) and rear (dorsal or posterior) “halves”, passing through the coronal suture “line”, running right to left across the external surface of the calvaria. The coronal suture represents the immobile joint between the frontal bone and parietal bones, and provides a basis for the name of our second reference plane, typically the coronal (or sometimes, frontal) plane. A third transverse plane, perpendicular to both the mid-sagittal and coronal planes, can be used to cut the body into top (rostral, superior or cephalic) and bottom (caudal or inferior) “halves”. Often, the transverse plane is centered in the vicinity of the umbilicus, though this is not a necessary placement. In fact, if we want to choose a frame of reference well-suited to the description of positions of the articulators (e.g., tongue, jaw and lips, relative say to the head), we might place the transverse plane in the vicinity of the caudal edges of the maxillary teeth, a plane dentists sometimes refer to as the maxillary occlusal plane.

Note that in the foregoing paragraphs, certain new terms -- dextral, sinistral, ventral, dorsal, rostral, and caudal -- were introduced to refer to directions associated with our three-dimensional Cartesian frame of reference. From this point on, these terms will provide unambiguous ways to indicate direction senses. Note that all lines perpendicular to the mid-sagittal plane “point” dextrally or sinistrally; all lines perpendicular to the coronal plane point ventrally (forward) or dorsally (backward); and, all lines perpendicular to the transverse plane point rostrally (up) or caudally (down). The mid-sagittal and coronal planes intersect to form a rostral-caudal axis; the mid-sagittal and transverse planes intersect to form a ventral-dorsal axis; and, the coronal and transverse planes intersect to form a dextral-sinistral axis.

The following are several terms that are common in descriptive anatomy that you will immediately begin to use. Get familiar with them and talk to your friends using them.

Planes of reference

Sagittal plane : Divides the body into right (dextral) and left (sinistral) halves. The mid-sagittal refers to a specific plane which is in the midline.

Frontal (Coronal) plane : Divides the body into front (anterior) and back (posterior) parts

Transverse (Horizontal) plane : Divides the body into upper (superior) and lower (inferior) parts

General Anatomical Terms

Ventral (Anterior) : toward the front of the bodyDorsal (Posterior) : away from the front of the body

Superficial (External) : toward the surfaceDeep (Internal) : away from the surface

Superior : upperInferior : lower

Rostral (Cranial) : toward the headCaudal : toward the tail

Medial : toward the axis or midlineLateral : away from the axis for midline

Proximal : toward the body or toward the root of a free extremityDistal : away from the body or the root of a free extremity

Central : pertaining to or situated at the centerPeripheral : toward the outward surface or part

Dextral : rightSinistral: left


Levels of Organization of the Human Body

An organism such as a human being is a highly complex structure that may be organized at a number of levels. Below are some traditionally defined levels of biological organization starting small and moving to the level of the organism.

Atoms, Molecules and IonsAtoms are considered to be the building blocks of matter. Atoms have a common structure made of protons, neutrons and electrons. The number of protons and neutrons in a given atom will define “what” that atom is. For example, hydrogen has a single proton and neutron. Atoms bind together in various ways to produce structures called molecules. For example, a water molecule is made of two hydrogen atoms and one oxygen atom. If an atom or molecule has an unequal number of electrons and protons, they will carry a positive or negative charge and are termed ions. Atoms, molecules and ions are the building block of cells, the basic unit of life. CellsThe cell is the smallest biologic unit that is considered to be living. The study of cells is called cytology. Cells are quite small (measured on the order of microns or thousandths of a mm) and plentiful (about 100 trillion in the average human). Because cells are living, they have a lifespan. A cell may live as long as the organism itself, as is the case of many neural cells. Alternatively, a given cell may lead a relatively short life and be subject to frequent replacement (e.g. skin cells). Cells contain a number of organelles that are necessary to sustain life activities.

TissueWhen cells and intercellular material (i.e. various molecules) are combined to produce some functional arrangement, we refer to it as tissue. The study of tissue is called histology. It is generally agreed that there are four basic types of tissue.

Epithelial Tissue: The main function of epithelial tissue is to cover the other bodily tissues. Epithelial tissue is characterized by a paucity of intercellular materials. The outer surface of the body is covered by epithelial tissue proper (i.e. skin). The inner surface of the body is covered with endothelial tissue. This includes the gastrointestinal tract and the lining of the lungs. Epithelial tissue proper and endothelial tissue is in direct contact with the environment. Body cavities such as the thoracic and abdominal cavities are lined with mesothelial tissue.

Connective Tissue: Connective tissue is a large category of tissues whose principle function is to provide structural support for the organism. In contrast to epithelial tissue, connective tissue is characterized by a lot of intercellular material. This is commonly referred to as the extracellular matrix. There are many types of connective tissue.

Loose Connective Tissue Areolar tissueAdipose tissue (FAT)

Dense Connective TissueTendons–attaches muscle to bone/cartilageLigaments–attaches bone to boneFascia – other supportive tissue

Special Connective TissueCartilageBone

Vascular tissueBloodLymphatic tissue

Muscle Tissue: Muscle is a tissue that has the capacity to generate force through contraction of tissue elements. There are three broad categories of muscle tissue that are differentiated based on their anatomical structure and function.


Striated muscle: Associated with voluntary movement

Smooth muscle: Associated with involuntary movement (e.g. GI system)

Cardiac muscle: Heart muscle

Nervous Tissue: Nervous tissue is a specialized tissue designed to generate, propagate and transmit electrochemical signals.

Organs or Tissue AggregatesWhen two or more tissues are combined to produce a functional unit, it is termed an organ. Examples of organs include the heart, the lungs, the kidney and the liver.

SystemsA system refers to a complex, organism-wide functional arrangement of organs/tissue aggregates. Outlined below are some primary bodily systems with a brief description of the tissues involved and the name given to the discipline that studies these systems. Those marked with an asterisk are particularly relevant for speech and swallowing.

Skeletal System*Bones and related cartilageOsteology

Articular System*Joints and ligamentsArthrology

Muscular System*Muscles and tendonsMyology

Nervous System*Brain, spinal cord, nerves, ganglia and sense organsNeurology

Respiratory System*Air passages and lungsPulmonology

Digestive System*Digestive tract and associated glands/organsGastroenterology

Cardiovascular (Circulatory) System*Heart, blood vessels, blood and lymphatic systemCardiology, Angiology

Reproductive SystemGenital tractsGynecology, Urology

Endocrine SystemDuctless glands of the bodyEndocrinology

Urinary SystemKidneys and urinary passagesUrology

Integumentary SystemSkin, nails and hairDermatology

Selected body systems relevant for Communication Disorders

The broad goal of this section is to provide a basic overview of selected bodily systems that are particularly relevant to the study of speech language pathology. We start with the circulatory system. For most of you this will be a review of information you probably learned in biology class. However, it is worth reviewing since in class and in the laboratory you will frequently come across arteries

and veins that provide the blood supply to key anatomical structures. In many cases, you will not be responsible for their names and what they supply. This is not true for the blood vessels within the central nervous system. I will want you to know this information in more depth because many communication disorders can result from problems with the circulatory system. However that


information will be handled in the last unit of the course. Second, there will be a brief introduction to the nervous system. We will return to this topic in much more detail at the end of the semester. Our goal at this point is to simply provide enough

information to get you through the next few units. Finally, we will move onto the muscular system. Since speech is the product of bodily movement, it is important for you to understand the basic function of muscle and how it is organized.

The Circulatory System

All cells in the body require nutrients and oxygen to function properly. Cellular function also produces products such as carbon dioxide that needs to be removed from the cell. Without this important function, the cells will die. As a result, there need to be a mechanism to deliver key chemicals to and from the cells of the body. Blood serves as a chemical transport system and the circulatory system is responsible for controlling blood flow through the body. The circulatory system consists of the heart, arteries, veins and capillaries.

The heart is principally a muscular structure that acts as a pump to move blood through the vascular (arteries, veins and capillaries) system. Arteries serve to take blood away from the heart. Veins return blood to the heart. Capillaries or capillary beds are small microscopic vessels that communicate between very small arteries (arterioles) and very small veins (venules). Arteries and veins have a different histological structure. Arteries have thick, firm walls that contain connective and (smooth) muscle tissue. Veins are thinner with less connective and muscle tissue. When in the laboratory, you will quickly note the differences in these structures, which helps in identification. The arteries retain their shape in the absence of blood. Veins tend to collapse. The Arterial and venous systems are each tree-like structures in that large vessels progressively branch into smaller and smaller vessels. The arterial tree and venous tree are connected by capillary beds. The main trunk of the arterial tree is a huge artery called the aorta. The main trunk of the venous tree is structure called the vena cava. Names are given to the branches of each. Over the course of the semester, you may be required to learn some of these branches. In

general, blood pumps from the heart to a network of arteries that get progressively smaller and smaller until they feed into capillaries, which then feed into the venous system which returns the blood to the heart. Capillaries are the site at which the important chemical exchange with surrounding tissue occurs. Therefore, every anatomical structure in the body will have a capillary bed that receives its blood supply by a particular artery(s) and drained by a particular vein(s).

In humans, the heart has four chambers. The left atrium and ventricle are interconnected as are the right atrium and ventricle. Blood enters the heat via the atria (plural for atrium) and leaves the heart via the ventricles. Following birth, the left and right side of the heart work as separate pumps that control two distinct circulatory circuits. The systemic circuit sends blood to and from all of the tissues of the body. A main function of the systemic circuit is to provide a supply of oxygen (O2) and other nutrients to the body and remove products of cellular metabolism (namely carbon dioxide or CO2) from the same tissues. Blood that has a relatively high concentration of O2 and a low concentration of CO2 is pumped from the left ventricle of the heart through the arterial system to the body. As the blood passes through the capillary beds, O2 diffuses into the tissues to allow cellular metabolism to occur. Simultaneously, CO2 and other metabolites diffuse into the blood. The blood then returns to the heart via the venous system with a relatively low concentration of O2 and a relatively high concentration of CO2. It enters the right atrium of the heart. The pulmonary circuit is responsible for moving this O2-depleted, CO2 rich blood (which gives the blood a dull, bluish appearance) to the lungs where CO2 can be removed from the blood


and O2 can diffuse into the blood. Blood leaves the right ventricle of the heart into the pulmonary artery which transports the blood to the lungs. Once gas exchange has occurred, the, now O2 rich blood (which has a bright red appearance) returns to the heart via the pulmonary vein and enters the left atrium of the heart. The blood pumps out of the heart via the left ventricle into the systemic circuit and the process repeats itself. In summary, a blood cell is on a continuous journey that takes the

following general route: left ventricle-systemic arterial system-capillary bed-venous system-right atrium-right ventricle-pulmonary artery-pulmonary capillary bed-pulmonary vein-left atrium-left ventricle. It should be noted that in the systemic circuit, which is much larger than the pulmonary circuit, arteries always contain O2 rich blood and veins always contain O2 depleted blood. The opposite is true for the pulmonary circuit.

The Nervous System

The nervous system (NS) is the source of stimulation (at least internal to the body) that causes muscles to contract, and eventually, causes all movements to occur. The NS is a huge topic, and in this course we can really only cover it in a very rudimentary way. There are several ways to slice and dice the NS, to make sense of it. From a structural (i.e., anatomical) point of view, we can

subdivide the NS into central and peripheral parts. In most reference sources, the central nervous system (or CNS for short) includes the brain and spinal cord. The peripheral nervous system (or the PNS for short) includes the bush-like conglomeration of cranial and spinal nerves, all their many sub-branches, and all peripheral sensors.

i. Cytology of the Nervous System

There are two broad cell types found in the nervous system. They are the neuron, and a group of cells collectively termed glia. The neuron typically gets all the press. To be sure, the neuron is the key to NS function, allowing us to do all the thinking, acting, (and speaking) that we do. Without it, I wouldn’t be able to stand in front of the class and entertain you the way I do (yeah right!). But as is often true in life, the star gets all the attention, and the supporting cast is barely acknowledged. To illustrate, the second edition of Kandel & Schwartz’s Principles of Neural Science (the “bible” of the nervous system) devotes a meager 15 pages of a 900-page text to the topic of glial cells. This seems even more meager when we learn that glial cells outnumber neurons by 10-50 times. Our remedy for this injustice is to begin our discussion of the NS cells with glia.

There are 3 main types of glial cells: The Schwann cell, the oligodendrocyte, and the astrocyte. Glial

cells (glia= “glue” in Greek) are considered to serve a number of functions. First, glial cells provide firmness and structure to the nervous system, much like connective tissue does in other parts of the body, and separates and insulates groups of neurons from each other. Second, some glial cells (i.e. astrocytes) have projections or “end feet” which serves to provide a physical barrier between the brain and the blood supply to the brain (blood-brain barrier). Third, glial cells provide a variety of “janitorial” services including (a) scavenging for cell debris that comes about from cell death and injury and (b) cleaning up potassium ions and chemical transmitters that float around in the extracellular space following neural activity. Fourth, glial cells provide myelin (i.e. oligodendrocyte in the CNS & Schwann cell in the PNS), the sheath that insulates nerve axons. Fifth, glial cells play an important role in guiding neuronal migration and axon growth during development. Finally, there is some more recent


evidence that glial cells have the potential to communicate in ways similar to neurons, suggesting that their NS role may be more than simply supportive. It may be that a comprehensive understanding of the nervous system will not be possible without a much-improved description of glial cell function.

The speech and hearing professional often hears about glial cells when things in the nervous system go wrong. Brain tumors often originate in glial tissue. The astrocytoma and glioblastoma are two types of tumors that can affect normal speech and hearing function.

ii. Somatic vs. Autonomic Nervous System

From at least one particular functional (i.e., physiological) point of view, we might also subdivide the NS into autonomic and somatic portions or systems. The autonomic subdivision of the NS is usually associated with involuntary motor behavior, involving “vegetative” functions that maintain life (e.g., digestion, cardiovascular action, respiration, glandular regulation). The autonomic system is usually subdivided into sympathetic and parasympathetic sub-systems, either on the basis of anatomical considerations, or functional ones. For example, most neurons and related nerve trunks that drive the sympathetic system are concentrated in the thoracic and lumbar regions of the spine -- hence the corresponding descriptive phrase thoracolumbar division. Neurons that drive the parasympathetic system are concentrated in cranial and sacral regions -- hence, the descriptive phrase craniosacral division. Some texts will suggest that the sympathetic and parasympathetic divisions of the autonomic system have antagonistic effects, in the sense that the sympathetic system is said to be

involved mostly in “alerting” reactions (e.g., accelerating the heart rate, constricting peripheral blood vessels), while the parasympathetic system is said to be involved in “calming” reactions (e.g., slowing the heart rate, dilating the blood vessels).

Since we have declared speech to be a voluntary act, we will largely ignore any other information about, or reference to the autonomic portion of the NS (though there is potentially a bit of an interest overlap, given our concern with respiration. Most of the time, we hope and assume that respiration happens “automatically,” and that we stay alive by breathing but never thinking about it or having to try to do it. In that sense, respiration for life seems to be vegetative and involuntary. You will come to learn, however, that speech respiration is significantly different from life respiration. The somatic subdivision of the NS is far more central to our interests, since it is usually associated with conscious, voluntary motor behavior.

iii. Afferent and Efferent Fibers of the PNS

In general, we can say that there are two main functions served by the conducting channels (e.g., nerves) in any major subdivision of the nervous system, including the peripheral somatic part. Efferent nerve fibers conduct information away from the central nervous system. Afferent fibers conduct information toward the central nervous system. When we speak of efferent nerves, we usually do so in a context of the so-called motor fibers that conduct excitatory impulses out to the

striated muscles, supplying and “driving” them to contract. When we speak of afferent nerves, we usually refer to conducting fibers that relay information back to the CNS, from sensory mechanisms distributed about the periphery. The four main types of peripheral sensory mechanisms (also, called receptors) are the mechanoreceptors, photoreceptors, chemoreceptors, and thermoreceptors. The names given to these receptor families suggest the types of stimuli that excite


them. Mechanoreceptors relay information about movement (kinesthesia), touch-pressure, sound (hair cells), and pain (nociception) back to the CNS. Photoreceptors-- obviously critical to the visual system -- respond to light. Chemoreceptors convey information about chemical processes (e.g., the changing “balance” between oxygen and carbon dioxide in the bloodstream that occurs during respiration). Thermoreceptors signal temperature and its changes. Mechanoreceptors, and to a lesser extent chemoreceptors, play significant roles in speech production. Photo- and thermoreceptors do not.

Two of the better-known mechanoreceptors that are important for kinesthesia* (sensation of movement, via the lengths of muscles, angles formed at joints, and forces applied to bones at tendinous interfaces) are the muscle spindle and the Golgi tendon organ. The spindle is a remarkable sensory mechanism, actually with its own muscle fibers and efferent motor supply that lies in parallel with other fibers in a (“parent”) muscle. When a muscle containing spindles is lengthened and stretched, the spindles (acting in their “passive” mode: i.e., assuming that their own muscle fibers do not also contract) will also be stretched, and will then discharge impulses, proportional to the stretch, that project back to that portion of the CNS where the motor neurons of the parent muscle reside. These impulses are excitatory to the parent muscle (and sometimes, some or all of its synergists). All else being equal, the spindle discharge will cause the parent muscle to contract, relieving the stretch on the spindles and surrounding, parallel muscle fibers. You are probably already familiar with the actions of muscle spindles, though you may not know it. For example, spindles in the superficial quadriceps femoris muscle of the ventral portion of the thigh underlie the familiar patellar tendon reflex (the ever popular knee-jerk response that we all can elicit when we “play doctor,” applying a gentle hammer to the tendon just below the knee cap or patella). In general, we can say that spindles provide information about muscle length, and the rate of change of muscle length. These are important

sensations, for at least two reasons. First, it is possible that we might sense the positions of parts of our body by “working out” the joint geometry implied by concurrent lengths of all our muscles. Spindles signal muscle length, and thus, provide a basis for this type of geometrical calculus. Second, it is also important to remember that the force-generating capability of striated muscle depends upon muscle length. An awareness of the ability of some muscle to generate force, for some future act, might easily be conveyed to the CNS -- and to the “Smart Little Person” who lives “in there” somewhere, who makes you do whatever you do -- by spindles that signal the current length of the muscle.

*The terms kinesthesia and proprioception are sometimes used as synonyms, sometimes not. According to The Bantam Medical Dictionary, kinesthesia is defined as the “sense that enables the brain to be constantly aware of the position and movement of muscles in different parts of the body,” while proprioception is mediated by “a specialized sensory nerve ending... that monitors internal changes in the body brought about by movement and muscular activity.” Given only these two statements, it is hard to tell the terms apart. For the near term, in SPPA 2050 we will use the two terms interchangeably.

The Golgi tendon organ is not as structurally elaborate, or as functionally complicated as the muscle spindle. The organ lies in the tendon of a muscle, near its bony origin and/or insertion, and senses the force generated within a contracting muscle. Its discharge is proportional to force, and is ultimately inhibitory to the parent muscle. In short, the Golgi organ “encourages” (in a passive, unintelligent way) the parent muscle to stop contracting. A decrease in the level of contraction of the parent would relieve strain transmitted to the sensor resulting from active or passive force generated within the muscle and sensed at the tendon. Golgi tendon organs are germane to SPPA 2050 interests in the general sense that we are interested in body movements (that cause variations


in air pressures and flows) that are themselves caused by forces generated within contracting muscle.

iv. Nerves of the peripheral nervous system

We usually subdivide the major nerves of the peripheral nervous system first into two groups, cranial and spinal. In most books, there are thirty-one (31) spinal nerves, and all of these are mixed with afferent and efferent fibers. Each spinal nerve takes its identifying initial-and-number from the regions of the spinal vertebra where it exits the spinal cord. We say that there are five types of vertebra – from top to bottom, Cervical (neck), Thoracic (thorax), Lumbar (curve of the lower back), Sacral (actually a midline vertebral complex integrated into the pelvis), and Coccygeal (your tail) – and correspondingly, five types of spinal nerves, identified by capital letters and Arabic numerals, and the same five main adjectives Cervical (eight in all, designated C1-8), Thoracic (twelve in all, designated T1-12), Lumbar (five in all, designated L1-5), Sacral (also five in all, designated S1-5), and Coccygeal (only one, referred to merely as the coccygeal nerve). Those spinal nerves that are of greatest concern in speech production are in the cervical, thoracic, and lumbar regions. These nerves provide motor supply to various thoracic and abdominal muscles relevant for respiration.

In broad terms, motor supply information -- defining which major nerve goes to which muscle -- is not all that hard to remember. Generally, the relative locations of muscles along a rostral-to-caudal axis through the body will give you some idea of their relative "level" of innervation (e.g., Cranial, supplies the head and neck, Cervical supplies the neck and upper limbs, etc). If you have difficulty remembering the motor supply for some specific muscle in the body, it is usually reasonable to guess at the answer, with the following top-down rule of thumb in mind: the higher the muscle along a rostral-to-caudal axis, the more likely the higher the supply. Of course, there are always some surprises (e.g., the ever-popular Diaphragm) that seem to be obvious counter-examples to the top-

down rule-of-thumb, but even considering those, you might still bat about .500 by guessing the level of innervation from the approximate location of a muscle along the rostral-caudal axis of the body.

There are twelve (12) cranial nerves, usually identified by a Roman numeral that is sometimes preceded by a capital letter “C.” Seven have relevance for speech and hearing. We will get into some of these later. I’d like you to be able to identify all of them, although not in the same level of detail. On the website there is a table that outlines all 12 cranial nerves and identifies those relevant for speech in bold. These nerves will be revisited at least two more times throughout this course. First, as we learn about the peripheral structures (in particular, the muscles) involved in respiration, phonation, and articulation, we will learn the innervation of these structures. Second, as we learn more about central nervous system structure and function, we will learn in more detail where these nerves originate in the brain.

And now, for a few words about plexuses...Certain nerves emerge separately from the central nervous system, but then “nest up,” cross, join, communicate, and intermingle to form indistinct “bundles.” These “bundled nerve nests” (my term, not anatomically standard) are called plexuses. A plexus represents a mixture of nerve roots that are truly distinct somewhere, but not where the bundles have "formed." The cervical spinal nerves, as a group, seem to be especially guilty of plexomania (again, my own editorial term, and definitely not a standard in anatomy). It is the custom in several texts to identify two major plexuses in the cervical spinal region -- the cervical (usually said to include roots from C1-C4) plexus, and the brachial (usually said to include roots from C5-C8). Perhaps the most famous nerve derived from the cervical plexus is the so-called phrenic nerve (formed from parts of


three cervical nerves, C-3, C-4, and C-5) that supplies (efferent) motor excitation to the diaphragm. (The careful reader will immediately notice a “contradiction” even in the last two sentences -- to wit, we say that the cervical plexus includes tracts from spinal nerves C1-C4, and then in the next breath, we say that the phrenic nerve, with contributions from C3-C5, is a component of the cervical plexus. Take this set of comments as a hint that the situation with plexuses is hardly ever

clear, or straightforward. For example, the brachial plexus is itself often subdivided into quite a few major branches -- the long thoracic, the thoracodorsal, the pectoral [medial and lateral] branch, the inferior and superior branches [often given other names], and so on. Oh, woe. Different texts say different things about plexuses. Don't get upset, or huffy. Just deal with the situation as best you can.)

The Muscular System

Muscle is the motor that “causes” all movement (as long as we (a) ignore the troublesome concept of free will; (b) take for granted some prior activity of the nervous system; and (c) disavow all other stimuli and forces “external” to the moving organism [e.g., wolves, elves, the wind, and whatnot]!). In humans, there are three kinds of muscle: (1) heart or cardiac muscle; (2) smooth (or “involuntary” muscle, e.g., that moves the gut, and the walls of blood vessels and certain of the “tubes” that make up the bronchial tree); and, (3) striated (or “voluntary”) muscle (e.g., the biceps brachii, diaphragm, and the ever-popular gluteus maximus). Sometimes, striated muscle is also called skeletal muscle. In the version of Speech Science you encounter in this class, striated muscle is more germane to our interests than other kinds of muscle, because we have declared speech to be a voluntary activity. A main purpose of this handout is to be sure you are aware of the basis for the name “striated” that is given to many muscles in the body . This information provides important insight about the structure and function of this type of muscle. [After this point, in this muscular introduction, the term muscle will be used simply to mean striated muscle.]

One of the pedagogical attractions of muscle is that it provides a good context for demonstrating that form and function are inter-related. If we simply examine the appearance of muscle, and couple our observations with a few simple “circumstantial” facts about its function, we can begin to make good

guesses about how and why muscle works as it does. At a gross level, a muscle is something like a package. The basic, standard package consists of a fleshy or meaty belly, wrapped in a membrane (fascia) called epimysium, attached to bone or cartilage at each of two ends by tendon. The bony attachment that is less mobile and often nearer the center of the body is referred to as the origin of the muscle. The attachment that is more mobile is usually referred to as the insertion. For example, the masseter muscle (look for this muscle in Netter) runs across the lateral surface of the lower jaw (i.e., mandible) -- a muscle’s line of action is usually the geometric line drawn through its “points” of origin and insertion. For the masseter, the origin is distributed across the zygomatic arch and temporal process of the zygomatic bone, and the insertion is distributed across the mandibular ramus and angle. Thus, its line of action runs from rostral and ventral, to caudal and dorsal. The masseter can generate force that “acts” along this line, and in this general direction. Muscles move bones (or whatever they happen to be attached to) not by pushing, but by pulling on them. If we have two bones that form a joint, like leaves of a hinge -- roughly, not unlike the joint formed between the mandible and skull -- and a muscle running between them, then one bone (We usually say the mandible.) will move toward the other (the rest of the skull) when the muscle is stimulated and allowed to “contract.” In this sense, contraction means that the muscle shortens in length. In simple geometric terms, the fact that the muscle shortens “explains” why one bone moves


closer to the other. The mandible moves toward (also, approximates, flexes or elevates toward) the skull when the masseter muscle contracts and shortens. The mandible moves away (also, extends or depresses away) from the skull, only if other muscles (e.g., anterior belly of the digastric, mylohoid, and/or geniohyoid muscles – look for them on different plates) contract and shorten to pull it in that direction.

In a more general sense, the term contraction is often used to refer to stimulation of muscle, and a subsequent generation of force by the muscle, independent of whether there is any change in muscle length. Thus, we speak of isometric contractions that produce force but do not involve any change in length of the muscle, and usually no movement of the structures against which the muscle pulls. We contrast these contractions with those that are anisometric, which create force and do involve some change in muscle length. It may interest you to know that a muscle can contract (in the sense of produce force) while shortening or lengthening. The extent to which any muscle contraction will cause movement will always depend upon the balance between the “pulling forces” generated within the muscle itself, and other forces that act on the structure that is pulled.

Across many joints (e.g., formed by bone 1-- say, the skull -- and bone 2 -- say, the mandible, from the preceding example) there will be one muscle that moves bone 2 one way with respect to bone 1, and an “opposing” muscle that moves bone 2 back the other way with respect to bone 1. The two muscles are mutually antagonistic. Their actions oppose one another. Each muscle is also said to be an agonist for its respective action. Often, there are multiple muscles that act about a joint, all potentially capable of producing the same motion. Each of these muscles is potentially an agonist for the motion, though one muscle among the group may “dominate” when the action is performed. We usually refer to “helper muscles” as synergists. Synergists may “operate” about the same joint as the “main mover,” or they may be distal to the joint,

but still assist in performing some action even they do not (and cannot?) “cause” that action directly.

A key, basic question to ask about contracting muscle is this: “Where does the force come from?” The answer is not “The Dark Side”. Instead, the answer comes to us from an examination of muscle structure. Suppose, out of idle curiosity, we start to (gently) pull a muscle apart. We find that a muscle belly separates relatively nicely into bundles of fibers that run more or less the length of the muscle. These bundles are called fasciculi, and each is wrapped in a membrane called perimysium. In turn, each fasciculus can also be subdivided longitudinally into a collection of muscle fibers, each wrapped separately in membranes referred to as endomysium. If we pull away the membranous cover that surrounds each muscle fiber, we then expose a collection of many small filaments, called myofibrils, running the length of the fiber, all lying side by side. One interesting fact about myofibrils is that they are not individually wrapped, in any way analogous to muscle fibers, fasciculi, or even (whole) muscles. A second interesting fact about the myofibrils is that if we view them in longitudinal section under a fairly high-powered microscope, we can see a pattern of “repeating stripes,”where the stripes run at right angles to the long direction of the myofibrils.

These stripes are the basis for the name striated. What do they represent? Each myofibril is itself composed of a collection of “stringy” protein molecules or filaments. There are basically two types, called actin and myosin, that also lie side by side. Neither type runs the length of the myofibril. Instead, both filament types are discontinuous, “running” for a little bit, and then stopping, and then running for a bit more, and stopping again, and so on. In a way, the regularly repeating “spans” of actin and myosin molecules are responsible for the striped appearance of muscle in a longitudinal section. We can divide each myofibril along its length into units called sarcomeres, each containing some myosin and some actin filaments, whose lengths partly overlap one another within the


sarcomere, but not completely. It is helpful to think of a myofibril as a string, made up of a series of cylindrical barrels or beads (i.e., the sarcomeres) joined end to end.Each sarcomere is about the same length as any other, and each sarcomere looks like any other, from the point of view of its stripes (i.e., its bands of light and dark “color”). By convention, the “boundary line” shared by any two adjacent sarcomeres is referred to as a Z line. Thus, each sarcomere is the collection of material (actin, myosin, and whatever else -- but certainly not air! -- that occupies intracellular space) lying between any two adjacent Z lines. Along the length of each sarcomere viewed in longitudinal section, there are these bands of color: (1) a relatively dark region (the A band) spanning maybe the middle two-thirds of the distance between Z lines, that may be slightly lighter in a narrow region (known as the H band) near the very middle of the sarcomere; and, (2) two relatively “lightish” regions (each half of an I band “shared” by two adjacent sarcomeres), one at each end of the sarcomere, falling between the end of the A band and the nearest Z line.

If we cut through or across a sarcomere, transversely or at right angles to the long axis of the myofibril, we discover that the bands correspond to regions filled by different proportions and arrangements of actin and myosin filaments. In the area of the I band, we find actin but no myosin filaments. In the area of the H band we find myosin but no actin filaments. In the darker portions of the A bands, we find both types of filaments apparently overlapping one another. We also come to realize that the A band corresponds to the length of the myosin filaments lying in the central portion of the sarcomere. There are many fine illustrations of this verbal description of the anatomy of a sarcomere, especially in physiology texts.

In the early 1950s, with the advent of electron microscopy, muscle biologists began to see directly for the first time that interesting things would happen to the lengths of some (but not all) “color bands” in sarcomeres when the length of a muscle

would change (e.g., as during anisometric contraction). We now know that if a muscle shortens, the lengths of the sarcomeres (i.e., the distances between adjacent Z lines), and their H bands and I bands also shorten, while the lengths of the A band remains the same. Similarly, if a muscle lengthens, the lengths of the sarcomeres, and their H bands and I bands, lengthen, but again the lengths of the A band remains the same. One way to understand these changes is to assume that actin and myosin filaments slide past one another as muscle length changes, increasing or decreasing their overlap (with muscle shortening or lengthening, respectively). This inference, completely correct, is typically referred to as the Sliding Filament Theory of Muscle Contraction.

We also know that the amount of force generated by contracting muscle after stimulation (e.g., from an electric shock, or more naturally, from nervous system activity), depends upon muscle length. This interdependence between muscle length and contractile force is known as the length-tension property of muscle. (Tension is another term that is often used to refer to the force generated by contracting muscle.) For many years, it has been known that at relatively short or relatively long lengths, a muscle produces less (active) force for the same level of stimulus applied to it than at intermediate lengths within the muscle’s “operating” range (i.e., its range of possible lengths). It is relatively easy, and correct, to leap to the idea that the force-generating ability of muscle depends in some way upon the degree of overlap of actin and myosin filaments within its sarcomeres. There are small “projections” that “stand off” the myosin filaments. When a muscle is stimulated, electrochemical events follow that allow these projections to “bind” to receptor sites on the actin filaments. These “bindings,” usually referred to as cross bridges, are the “source” of (active) force we receive from contracting muscle. Momentarily, after stimulation, it is as though the myosin filaments “lock” onto the actin filaments. The arrangement of the myosin projections that “lock” into actin binding sites will actually pull and slide


the actin filaments toward the center of the sarcomere, causing the muscle to shorten, as long as no force greater than that produced by the contraction is applied to both ends of the muscle.

We thus gain some insight into the length-tension property of muscle -- a key feature of striated muscle function -- by examining the form of its sarcomeres (i.e., the degree of overlap of actin and myosin) at the moment the muscle is stimulated to contract. At some optimum, intermediate length of the sarcomere, the number of cross bridges that can form between actin and myosin filaments is at a maximum. This length corresponds to the “peak” of the “active portion” of the so-called length-tension curve (roughly speaking, a curve that looks something like the bell-shaped curve representing the normal distribution in statistics). At sarcomere lengths greater than this optimum length, the filaments do not overlap as much, and fewer cross bridges (and thus, less contractile force) are possible. At sarcomere lengths less than the optimum length, filaments over-lap too much, in the sense that actin filaments from opposite ends of the sarcomere “crowd” (i.e., overlap) one another, and myosin filaments collide against the Z-line boundary at each end of the sarcomere.

The stimulus that excites muscle, and causes it to contract, comes from nerve cells called motor neurons. Each motor neuron, in the brain or spinal chord, has a nerve fiber called an axon -- if you like, a kind of “insulated electrical chord” -- that leads away from it and toward the part of the muscle the neuron stimulates. Individual neurons don’t “drive” whole muscles. Instead, each neuron is responsible for stimulating some specific subset of the muscle fibers in a muscle, usually distributed across some portion of the muscle rather than lying together, side by side, in a clump. We often say that a pool of motor neurons within the central nervous system is responsible for driving all the muscle fibers in any particular muscle. Some neurons are “tied” by their axons to single muscle fibers, while other neurons are “tied” to, and responsible for stimulating, many (e.g., even hundreds of) muscle

fibers. We refer to the combination of a motor neuron, its associated axon, and the collection of muscle fibers it stimulates (or innervates), as a motor unit (often abbreviated MU). The “size” of the motor unit depends upon the number and cross diameters of all fibers that belong to it, and in an obvious way, is related to the amount of force the motor unit will deliver when it contracts. This is merely because the total cross sectional area of the muscle fibers belonging to the unit is a straightforward index of the number of cross bridges that can form, as long as all muscle fibers belonging to all motor units within the same muscle are about the same length.

The motor unit is the smallest functional unit within striated muscle. We say this for the following reason: When a stimulus from a motor neuron is delivered to its muscle fibers, at some time we might call t0, essentially all sarcomeres within all myofibrils within all affected muscle fibers respond in the same way by contracting simultaneously, forming the maximum number of cross bridges subject only to the degree of overlap between actin and myosin filaments. If the stimulus is “isolated” (i.e., a “one-shot instruction” to contract), the motor unit responds with a twitch, a brief increase in force that dies out over time. It takes a little time after the stimulus at t0 for the contractile force to build up, and then a little bit of time for the force derived from that stimulus to dissipate. How much time depends upon the specific chain of electrochemical events that allows formation and dissociation of the actin-myosin cross bridges. Some motor units, even within the same muscle, twitch faster than others because of their intrinsic biochemistry. The “twitch speed” -- in effect, an index of how rapidly force builds up in a MU after it is stimulated -- is often described in terms of the time to peak tension after the moment of stimulation. The fastest “twitching” motor units in the human body (e.g., those MUs in muscles that control positioning of the eye, and other tiny structures) reach peak tension in about 15 ms. Very slow twitching motor units (e.g., in leg muscles that are responsible for maintaining posture) reach peak tension in about 150-200 ms.


Any specific motor unit will twitch (almost) exactly the same way each time it is stimulated to contract. The force that its contraction can contribute to some behavior depends solely upon the number of possible cross bridges that can form amongst all of its fibers’ myofibrils’ sarcomeres. Over time, we can obtain more force from an MU than the amount given by its isolated twitch, if we stimulate the MU to contract at a rate faster than the time it takes for its isolated twitch response to die out. Twitch responses from closely repeating stimuli, delivered to the same motor unit, will “ride up on top of one another,” summing to create a bigger force (at some time after the initial stimulation) than is possible from an isolated twitch. Conceptually, then, one way to vary or grade the force output from contracting muscle is to vary or grade the rate at which motor units within the muscle are stimulated. When this happens -- and it happens all the time when we voluntarily increase the strength of contraction of a muscle -- we say that we have increased the firing frequencies of the active MUs.

Another way to grade the force output of muscle, conceptually speaking, is to vary the number of MUs that are being stimulated at any one time. Not all motor neurons within the pool associated with some whole muscle will send their excitatory instructions to their respective motor units at the same time, in either a narrow or broad sense. At any one time, some proportion of the motor units in the “parent” muscle may be contracting. The greater the number of units that are contracting, the greater the total force output from the muscle. Conversely, the lower the number of units contracting, the lower the force output. During voluntary muscle contractions, where total force increases over time, the number of motor units that are “recruited” to the task also increases over time. This is a phenomenon that is easy to demonstrate (with appropriate machinery, to “listen in” on the concurrent activity of several contracting MUs), and enlightening to perceive.

Top-10 List of Things to Remember about (Striated) Muscle:

10. A few simple “size facts” about muscle. It comprises ~40 % of body weight. Fibers are 10-100 microns in diameter and range from 1 to 120 mm long. MUs can contain up to 100s of fibers. Sarcomeres are ~3 microns long.

9. A muscle belly, wrapped in epimysium and connected by tendon to bone, is made of parallel fibrous bundles called fascicles, wrapped in perimysium, made of parallel bundles called fibers, wrapped in endomysium, made of parallel filaments called myofibrils, made of (serial) chains of repeating sections called sarcomeres.

8. The repeating pattern of "stripes" that cannot be seen by the naked eye, but that give striated (voluntary) muscle its name, represent repeating arrangements of thick (myosin) and thin (actin) filaments within every sarcomere along the length of a myofibril.

7. When muscle contracts (and shortens), actin filaments attached to both ends of each sarcomere, and myosin filaments arrayed in the central part of each sarcomere, slide past one another.

6. Only (anisometric) muscle contractions involving changes in muscle length can cause movement (of one body part with respect to another). There are special "contractions" involving changes in force but no change in length that are identified by the special name isometric.

5. The active force arising from muscle when it is stimulated depends specifically upon the degree of overlap (and thus, the extent of cross-bridge formation) between actin and myosin filaments within sarcomeres. This fact is at the root of the Length-Tension Property of every muscle.

4. All sarcomeres within the myofibril, and all myofibrils within the muscle fiber, respond (and contract) in the same way when the fiber is


stimulated. But only a subset of fibers within a fascicle contract when the fascicle is stimulated, if that stimulus is "delivered" to the fascicle by means of one or some of the pool of motor neurons supplying the muscle as a whole.

3. The set of muscle fibers all innervated by the same motor neuron, the neuron itself, and its associated axon (nerve fiber) make up what is known as the Motor Unit (MU). This is the minimal functional unit within muscle, which responds in an all-or-none fashion to stimuli applied to it. If too weak a stimulus is applied (actually and initially, directly the the motor neuron), the MU will not respond (and contract) because the motor neuron will not “send a signal” to its muscle fibers to contract. If a sufficiently strong, isolated stimulus is applied, the MU will respond with an invariant twitch whose amplitude (peak force) and time history are exactly the same for every sufficient stimulus (assuming that the MU has not been “fatigued” by too many preceding stimuli). MUs vary in several interesting ways, within and across muscles of the body:

(a) Some MUs are “large,” with large numbers of fibers and thus, a capability for large twitch tensions. Other MU's are small.(b) Some MUs (fight-or-flight?) fatigue rapidly (lose the ability to produce any tension, even when stimulated) when driven rapidly and repeatedly; other MUs (postural units?) are highly resistant to fatigue.(c) Some MU's, usually in muscles that move small loads, have relatively fast times to peak tension in their twitch response (15-30 ms); other MU's contract a good deal more slowly (100-150 ms, to peak tension).

2. The active force generated by contracting muscle can be "graded" (increased or decreased) by either or both of two mechanisms:(a) changes in firing frequency of active MU's, and/or (b) increases (or decreases) in the number of MU's recruited to task.

And the #1 fact to remember about muscle is...

1. Muscle is the motor by which all voluntary movement takes place.

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CHAPTER Ihomepages.wmich.edu/~stasko/sppa205/unit1notes.doc · Web viewPathologic anatomy/pathology: Concerned with the effect of disease on anatomical structure. These may include