The Skeletal System

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Skeleton: Overview

o Functions of the Skeleton• Support• Protection• Blood cell production• Storage• Movement

o Anatomy of a Long Boneo Bone Growth and Repairo Surface Features of Bones

Skeleton: Overview

o Classification• Long – longer than

they are wide• Short – cube

shaped• Flat – plate-like,

with broad surfaces

• Irregular – varied shapes

• Round – circular in shape

Fig 6.1

Skeleton: Overview

o Anatomy of a Long Bone• Periosteum – tough,

connective tissue covering

• Epiphysis – expanded portion at the ends of bones

• Diaphysis – portion between the epiphyses

• Medullary cavity – hollow portion of diaphysis containing yellow marrow

• Articular cartilage – layer of hyaline cartilage where bones join together

• Endosteum – lines the medullary cavity and the spaces of spongy bone

Skeleton: Overview

• Compact Bone Lacunae – contain bone cells (osteocytes) Lamellae – concentric layers of matrix containing

collagen fibers and mineral salts Blood vessels and nerves enter the central canal

• Spongy Bone Contains bony bars and plates called trabeculae Trabeculae follow lines of stress, giving bones strength

Fig 6.2b

Skeleton: Overview

o Bone Growth and Repair• Osteoprogenitor cells – unspecialized

cells• Osteoblasts – bone forming cells• Osteocytes – mature bone cells• Osteoclasts – break down bone

Skeleton: Overview

• Bone Development and Growth Ossification – formation of bone

Intramembranous ossification Bone forms between two sheets of fibrous

connective tissue Form bones of the skull

Endochondral ossification Form most bones of the human body Hyaline cartilage models are replaced by

bone Epiphyseal plate

Band of cartilage in the epiphyses of long bones Long bone growth continues until plate is

ossified Appositional growth – increase in bone

diameter

Fig 6.3

Skeleton: Overview

• Remodeling of Bones Bone is continually being broken down

and built up again Osteoclasts remove worn cells and

deposit calcium in the blood Osteoblasts remove calcium from the

blood and form new bone Three important hormones regulating

bone growth Parathyroid hormone Calcitonin Growth hormone

Skeleton: Overview

• Bone Repair Required after it fractures (breaks) Steps involved in bone repair

Hematoma Fibrocartilaginous callus Bony callus Remodelling

Naming of fractures Complete – bone is broken through Incomplete – bone is not separated into two parts Simple – does not pierce the skin Compound – pierces the skin Impacted – broken ends are wedged into each other Spiral – ragged break due to twisting of bone Reduction – repair of a fracture

Closed reduction – re-aligning bone fragments without surgery

Open reduction – surgical repair of the bone using plates, screws, or pins

Fig 6.4

Table 6.1

Fig 6.5

Axial Skeleton

o Lies in the midline of the bodyo Bones of the axial skeleton

• Skull• Hyoid bone• The vertebral column• The thoracic cage• Middle ear bones

Axial Skeleton

• Skull Formed by the cranium and the facial

bones Sinuses

Air spaces within the bones Lined by mucous membranes Reduce the weight of the skull Give the voice a resonant sound Paranasal sinuses

Maxillary Frontal Sphenoidal Ethmoidal

Mastoid sinuses

Fig 6.6

Axial Skeleton

• Bones of the Cranium Protects the brain Sutures – immovable joints Composed of eight bones

Frontal bone Parietal bones Occipital bone Temporal bones

External auditory meatus Mandibular fossa Mastoid process Styloid process Zygomatic process

Sphenoid bone Ethmoid bone

Crista galli Cribriform plate Perpendicular plate Superior and middle nasal conchae

Fig 6.7bFig 6.7a

Fig 6.8bFig 6.8a

Axial Skeleton

• Bones of the Face Maxillae

Alveolar process Palatine process

Palatine bones Zygomatic bones Lacrimal bones Nasal bones Vomer bone Inferior nasal conchae Mandible

Mandibular condyle Coronoid process

Skeletal Muscles of the Body

• Hyoid bone Superior to larynx Only bone in the

body that does not articulate with another bone

Anchors the tongue Site of attachment

for muscles associated with swallowing

Fig 6.5a

Axial Skeleton

• Vertebral Column (Spine) Supports rib cage Serves as a point of attachment for the

pelvic girdle Protects the spinal cord Consists of a series of separate bones

named for their location Seven cervical (neck) Twelve thoracic (chest) Five lumbar (lower back) Five sacral Three to five coccygeal

Normal curvatures

Fig 6.9

Axial Skeleton

Normal curvatures Cervical and lumbar – convex anteriorly Thoracic and sacral – concave anteriorly Provide support and balance Abnormalities

Lordosis – exaggerated lumbar curvature Kyphosis – increased roundness of the

thoracic curvature Scoliosis – abnormal lateral curvature that

occurs most often in the thoracic region

Fig 6.10

Axial Skeleton

• Intervertebral Disks Prevent vertebrae from grinding against one

another Absorb shock Allow motion between vertebrae

• Vertebrae Body – anterior portion Vertebral foramin – canal for spinal cord Bony projections serve as sites for muscle

attachment Atlas (C1) – supports the head; allows head

movement up and down Axis (C2) - serves as a pivot for the atlas; allows

head movement from side to side Sacrum – fused sacral vertebrae; forms posterior

wall of the pelvic cavity Coccyx – formed from a fusion of three to five

vertebrae

Fig 6.11

Axial Skeleton

• The Rib Cage Protects the heart and lungs Provides support for the bones of the pectoral

girdle The ribs

Twelve pair that connect to the thoracic vertebrae True ribs – upper seven pairs connect directly to the

sternum by costal cartilages False ribs – next five pair that attach indirectly to the

sternum or not at all (“floating” ribs) The sternum

Flat, blade-shaped bone Composed of three bones that fuse

Manubrium Body Xiphoid process

Fig 6.12

Appendicular Skeleton

o Pectoral Girdle• Clavicles

Articulate medially with the manubrium Only attachment to the axial skeleton Serves as a brace for the scapula and

stabilizes the shoulder

• Scapulae Spine Acromion process Coracoid process Glenoid cavity

Fig 6.13

Appendicular Skeleton

o Upper Limb• Humerus

Long bone of the arm Head articulates with the glenoid cavity of the

scapula Greater and lesser tubercles serve as attachments

for muscles Intertubercular groove holds a tendon from the

biceps brachii Deltoid tuberosity attaches the deltoid Capitulum articulates with the head of the radius Trochlea articulates with the ulna Coronoid fossa Olecranon fossa

Fig 6.14

Appendicular Skeleton

• Radius Lateral side of the forearm Head articulates with the capitulum of the humerus and

fits into the radial notch of the ulna Radial tuberosity attaches a tendon from the biceps

brachii Ulnar notch articulates with the head of the ulna Styloid process attaches ligaments that run to the wrist

• Ulna Longer bone of the forearm Coronoid process articulates with the coronoid fossa

when elbow is flexed Olecranon process articulates with the olecranon fossa

when the elbow is extended Trochlear notch articulates with the trochlea of the

humerus Head articulates with the ulnar notch of the radius Styloid process attaches ligaments that run to the wrist

Fig 6.15

Appendicular Skeleton

• Hand Wrist (carpus) contains eight small bones Metacarpal bones form the palm Phalanges

Bones of the fingers The thumb has only two phalanges (proximal

and distal) The other fingers have three phalanges each

(proximal, middle, and distal)

Fig 6.16

Appendicular Skeleton

o Pelvic Girdle• Coxal bones

Ilium Ischium Pubis

Pubic symphysis Obturator foramen

• Gender differences Female has broader hips Female pelvis is wider Female inlet and outlet of the true pelvis are wider Female pelvic cavity is more shallow Female bones are lighter and thinner Female pubic arch is wider

Fig 6.17

Appendicular Skeleton

o Lower Limb• Femur

Longest and strongest bone in the body Head fits into acetabulum of coxal bone Greater and lesser trochanters attach

muscles of the thigh and buttocks Linea aspera attaches several muscles Medial and lateral epicondyles attach

muscles and ligaments Lateral and medial condyles articulate

with the tibia Patellar surface articulates with the

patella

Fig 6.18

Appendicular Skeleton

• Tibia Medial bone of the

lower leg Bears the weight from

the femur Medial and lateral

condyles articulate with the femur

Tibial tuberosity attach patellar ligaments

Anterior crest Medial malleolus

articulates with the talus in the foot

• Fibula Lateral to the tibia Stabilizes ankle

Fig 6.19

Appendicular Skeleton

• Foot Seven tarsal bones Only the talus can

move freely The calcaneus and the

talus support the weight of the body

Five metatarsal bones form the instep

The phalanges form the toes Big toe has only two Three each in other

toes

Fig 6.20

Joints (Articulations)

o Classification according to the amount of movement

• Synarthrosis – immovable• Amphiarthrosis – slightly moveable • Diarthrosis – freely moveable

o Classification according to structure

• Fibrous • Cartilaginous • Synovial

Joints (Articulations)

• Fibrous – fibrous connective tissue Fibrous connective tissue joins bone to

bone Typically immovable Sutures of the cranium

Coronal – between the parietal bones and the frontal bone

Lambdoidal – between the parietal bones and the occipital bone

Squamosal – between each parietal bone and each temporal bone

Sagittal – between the parietal bones Joints formed by each tooth in its socket

Fig 6.8Fig 6.7

Joints (Articulations)

• Cartilaginous Bones are joined by fibrocartilage or

hyaline cartilage Usually slightly moveable

• Synovial Bones do not touch each other Bones are separated by a joint cavity Usually freely moveable

Fig 6.22Fig 6.21

Joints (Articulations)

Types of synovial joints Saddle joint Ball-and-socket joint Pivot joint Hinge joint Gliding joint Condyloid joint

Fig 6.23

Joints (Articulations)

Movements permitted by synovial joints Angular movements

Flexion Extension Adduction Abduction

Circular movements Circumduction Rotation Supination Pronation

Special movements Inversion and eversion Elevation and depression

Fig 6.24

Effects of Aging

o Cartilage and bone tend to deteriorate

o Articular cartilage may not function properly, resulting in arthritis

• Osteoarthritis – deterioration of the articular cartilage

• Rheumatoid arthritis – synovial membrane becomes inflamed

• Gout – excessive buildup of uric acid

o Osteoporosis is common

Homeostasis

o Functions of the Skeletal System• Protection of internal organs• Bones assist in all phases of

respiration• Bones store and release calcium• Bones assist the lymphatic system

and immunity• Bones assist digestion• The skeleton is necessary to

locomotion

Homeostasis

o Functions of Other Systems• The integumentary and the muscles

assist in protecting internal organs• The digestive system absorbs calcium

from food and the endocrine system regulates the storage of calcium in the bones

• Movement of the bones is only possible because of the contraction of skeletal muscle