The Skeletal System

The Skeletal System Organs – bones, joints, cartilage,

ligaments

FunctionsA. Support – hard framework that supports

and anchors all soft organs of the body – Ex. Legs act as pillars to support trunk, rib cage supports thorax wall

B. Protection – skull protects brain, ribs protect heart/lungs, zygomatic arch protect the eye

C. Movement – skeletal muscles, attached to bone by tendons, used the bones as levers to move the body and it’s parts; arrangement of bones and the design of joints determine the types of movement possible

Functions (con’t)D. Storage

Fat stored in the internal cavities Bone matrix stores minerals (Ca+2) –

“deposits” and “withdrawals” of minerals to and from bones goes on almost continuously

E. Blood cell formation (hemopoiesis) Carried on in red bone marrow; hemopoietic

tissue – Fig. 6-5 Hemopoietic tissue is found in the ends of

long bones Transformed to yellow bone marrow, an inactive

fatty tissue, as person ages

Classification of BonesA. Classified according to shapeB. Contain different proportions of

1. Compact bone (smooth & homogeneous)

2. Spongy (cancellous) bone – spaces & trabeculae (beams)

Classification of BonesC. Long bones

1. Longer than they are wide

2. Consists of a shaft plus two ends 3. Primarily compact bone; but may contain

substantial amounts of

spongy bone

Classification of BonesD. Short bones

1. Roughly cube-like – ex. Wrist/ankle 2. Mostly spongy bone; compact bone only

provides a thin surface

Classification of BonesE. Flat Bone

1. Thin, flattened and usually a bit curved –

sternum, ribs, most skull bones2. Two roughly parallel compact bone

surfaces with a layer of spongy bone between

Classification of BonesF. Irregular bones – some skull, hip,

vertebrae1. Fit none of the preceding classes2. Complex shapes3. Mainly spongy bone enclosed by thin layers

of compact bone

G. Sesamoid bones –a special type of short bone

embedded within a tendon; ex. - patella

Bone Structure – 2 levelsA. Gross Anatomy – What you can see with the naked eye - Fig. 6-1B. Microscopic Anatomy – Fig. 6-2, 6.3

Gross AnatomyLong Bone – most have the same basic structure

1. diaphysis (shaft) – hollow tube of hard compact bone2. medullary cavity – hollow area; contains yellow bone marrow3. epiphyses – bone end or extremities; usually more expanded

than diaphysis; thin layer of compact bone forms exterior;interior spongy bone filled with red bone marrow4. epiphyseal line/plate – remnant of cartilage present at junction of diaphysis & epiphyses in young bones; growthare that allows bones to lengthen5. articular cartilage – found where long bones articulate (join);cushions the bone ends and absorbs stress during joint movement6. periosteum – outer surface of diaphysis; richly supplied withnerve fivbers, lymphatic vessels, and blood vessels which entervia nutrient canals7. endosteum – fibrous membrane that lines medullary cavity

Gross Anatomy

Microscopic AnatomyCompact bone – Fig. 6-2, 6-3

1. Haversian system – structural unit; circular 7 tubelike;composed of calcified matrix arranged in multiple

layers (one inside the other – like an onion)2. osteocytes (bone cells) – regulate the removal of calcium from

bone matrix

Osteocyte (within lacuna)

Microscopic AnatomySpongy bone

1. Trabeculae – structural unit2. Osteocytes – only a few cell layers thick; no Haversian system3. Nutrients reach osteocytes by diffusion

Microscopic AnatomyCartilage – Fig. 6-4

1. Fibers embedded in gel (not calcified matrix)2. Chondrocytes (cartilage cells)3. Cartilage contains no blood vessels; nutrients diffuse

through matrix4. Function

a. supports & reinforcesb. cushioning propertiesc. resists compressive stress (articular

cartilage)

Microscopic Anatomy

Bone Development(osteogensis) – Fig. 6-5

A. Intramembranous ossification – flat bones form from fibrous membrane – ex. Skull, clavicle, ribs

B. Endochondral ossification – bone formation from hyaline cartilage structures; most bones form this way;

osteoblasts – bone forming cellsosteoclasts – bone reabsorbing cells

Endochondral Ossifcation – Fig.

Cartilage model is the starting point

Endochondral Ossifcation – Fig.

Formation of a bone collar around the shaft of the hyaline cartilage model

Endochondral Ossifcation – Fig.

Cartilage matrix calcifies; chondrocytes die

Endochondral Ossifcation – Fig.

Invasion of internal cavities by periosteal bud and spongy bone formation (3 mo. embryo)

Endochondral Ossifcation – Fig.

As the primary ossification enlarges, osteoclasts break down spongy bone & form medullary cavity

Ossification of epiphyses- development of secondary ossification centers in epiphyses;

cartilage begins to become bone- when complete cartilage remains only at epiphyseal surfaces

(articlular cartilage) and at the epiphyseal plate

Endochondral Ossifcation – Fig. 6-5

Bone growth continues during infancy & youth- long bones lengthen at epiphyseal plate- long bones thicken by a process called appositional growth (inside breaks down at a

slower rate than exterior builds up)- some facial bones (nose, mandible) grow

throughout life

Endochondral Ossifcation – Fig. 6-5

The Skeleton – 206 bones

Axial skeleton – forms long axis of body & includes the bones of the skull, vertebral column, and rib cage

Appendicular skeleton – bones of upper and lower extremeties and girdles (shoulder/hip)

The Axial Skeleton – 80 bonesA. Skull – body’s most complex bony

structure – Fig. 6-81. Cranial bones (8)

a. site of attachment of head muscles

b. enclose & protect brain & organs of hearing & equilibrium

Cranial Bones (red highlight)

The Axial Skeleton – 80 bones2. Facial bones (14)

a. form framework of faceb. hold eyes in an anterior positionc. provide cavities for the organs of

taste & smell and openings for the

passage of air & food

d. secure teethe. anchor the facial muscles of

expression

Facial Bones (black & nasal concha)

The Axial Skeleton – 80 bones3. Middle ear bones (6) – used in sense of

hearing

The Axial Skeleton – 80 bones4. Sutures – interlocking joints of skull

bones

The Axial Skeleton – 80 bonesB. Vertebral column – 26 irregular bones

that form a flexible curved rod that supports the body trunk1. Provides attachment points for ribs &

muscles of back2. Division of spine – curvature increases

strength, resilience & flexibility of spine,

making it function like a spring rather than

a rod

Vertebral Column

The Axial Skeleton – 80 bonesC. Thorax – 12 pairs of ribs (both male &

female),sternum, thoracic vertebrae, costal cartilage1. Forms protective cage around thoracic organs2. Supports shoulder girdles & upper limbs3. Provides attachment points for the muscles

of the back, chest, & shoulders4. Intercostal spaces – occupied by inter-

costal muscles which elevate & depress

during breathing

Rib Cage

The Appendicular Skeleton 126 bones

A. Adapted to carry out movementB. Pectoral (shoulder) girdle – clavicle,

scapulaC. Arm/hand – humerus, radius, ulna,

carpals, metacarpals, phalangesD. Pelvic girdle – coxal bones (ilium,

ischium, pubic)E. Leg/feet – femur, tibia, fibula, patella,

tarsals, metatarsals, phalanges

The Appendicular Skeleton Pectoral Girdle

The Appendicular Skeleton Arm/hand

The Appendicular Skeleton Pelvic Girdle

The Appendicular SkeletonLeg/feet

Male & Female Skeletal Differences

A. Most male skeletons are larger (no great functional importance)

B. Structural difference in pelvis1. Male - narrower2. Female – structured to cradle baby; broader, shallower,lighter, rounder

C. Pelvic brim1. Male – basically heart shaped2. Female – wider, oval from side to side

D. Coccyx1. Male – narrow, longer; less movable; curves ventrally2. Female – wider, shorter; more movable; straighter

Male & Female Skeletal Differences

Male & Female Skeletal Differences

Articulations (joints)

Two different ways to classifyStructural classification – based on material that

bindsfibrouscartilaginoussynovial

Functional classification – based on amount of movement

Articulations Synarthroses – immovable joints; fibrous

connective tissue grows between the articulating bones; - ex. Sutures of cranial bones

Articulations Amphiarthroses – slightly moveable; cartilage or

fibrous tissue connects articulating bones – ex. Symphysis pubis, ligaments, fibrous membrane between radius & ulna

Articulations Diarthroses – allow considerable movement; Fig. 6-20, 6-21,

Table 6-71. Ball & socket

a. shoulder & hip jointsb. this type of joint permits the widest range of motion

Articulations Diarthroses – allow considerable movement; Fig. 6-20,

6-21, Table 6-72. Hinge joints

a. elbow & knee, fingers, toesb. movement in 2 directions – flexion (bending), extension (straightening)

Articulations Diarthroses – allow considerable movement; Fig. 6-20, 6-21,

Table 6-73. Pivot joint

a. small projections of one bone pivots in an arch of anotherb. C2 (axis) projection pivots in arch of C1 (atlas); allows rotation of the head

Articulations Diarthroses – allow considerable movement; Fig.

6-20, 6-21, Table 6-7 4. Saddle Joint – only 1 pair

a. between metacarpal bone of thumb & carpal bone of the wristb. produces great mobility (opposable thumb);

flex & extend Abduct – moving away from midline Adduct – moving toward midline Circumduct - circle

Articulations Diarthroses – allow considerable movement; Fig.

6-20, 6-21, Table 6-75. Gliding – flat surfaces

a. least movable of all diarthrotic joints

b. joint between vertebrae or between

& carpal/tarsal bones

Articulations Diarthroses – allow considerable movement; Fig.

6-20, 6-21, Table 6-76. Condyloid joints (ellipsoid)

a. condyle fits into an elliptical socket

b. ex. – distal end of radius & carpal

bones or femur & tibia