Skeletal System/Bones

Functions of bone

1. Structural support: posture

2. Protection: heart, lungs, brain

3. Mineral storage: calcium and phosphorous

4. Blood cell formation (Hemopoiesis): in bone marrow

5. Movement: points of attachment and serve as levers

How many bones are present?

206 bones total

-177 bones for voluntary movement

-29 bones immobile

2 Major Skeletal Sections

Axial

Appendicular

Axial Skeleton

80 bones

• skull

• vertebral column (spine)

• sternum

• ribs

Appendicular Skeleton

126 bones

• upper extremity

• lower extremity

• shoulder girdle

• pelvis

Composition of bone tissue

calcium carbonate and calcium phosphate (60-70% of bone)

collagen (protein)

water (25-30% of bone)

Calcium carbonate and calcium phosphate role in bones

gives bone its stiffness and ability to withstand compression

Collagen role in bones

gives bone its elasticity and tensile strength

Types of Bone

Compact

Cancellous

Compact bone

hard, dense outer layer of all bone

opaque upon x-ray

Cancellous bone

less dense, porous or spongy

less opaque upon x-ray

latticework of inner portion of bone

trabecular systems

Long bone

serve as levers

create framework for body

makes movement possible

Short bone

shock absorption

no diaphysis

fairly symmetrical

ex: carpals, tarsals

Flat bone

protection

flat surface

ex: bones of skull, pelvis

Irregular bone

variety of purposes

cannot be classified as long, short, flat or sesamoid

ex: cervical (7 vertebrae), thoracic (12 vertebrae), lumbar (5 vertebrae), sacral (5 vertebrae-fused), coccyx (4 vertebrae-fused)

Sesamoid bone

protection, mechanical advantage

Diaphysis

long cylindrical shaft

Cortex

hard, dense compact bone forming walls of diaphysis

Periosteum

dense, fibrous membrane covering outer surface of diaphysis

Endosteum

fibrous membrane that lines the inside of the cortex

Medullary cavity

between walls of diaphysis containing yellow or fatty marrow

blood cell formation

Metaphysis

wider portion between the diaphysis and epiphysis

Epiphysis

ends of long bones formed from cancellous bone

Epiphyseal plate

growth plate; thin cartilage plate separates diaphysis and epiphyses

Apophyses

bony process with an independent center of ossificiation and associated growth plate, which serves as a point of attachment for a ligament or tendon

Long bones of skeleton in upper extremity

1. Clavicle

2. Humerus

3. Ulna

4. Radius

5. Metacarpals

6. Phalanges

Long bones of lower extremity

1. Femur

2. Tibia

3. Fibula

4. Metatarsals

5. Phalanges

Processes

elevations or projections

Processes that form joints

Head - prominent rounded projection (head of humerus)

Condyle - large rounded projection (medial/lateral condyles of femur)

Facet - small, nearly flat surface (articular facets of vertebra)

Processes to which muscle, ligaments or tendons attach

Tubercle

Tuberosity

Trochanter

Spine

Epicondyle

Crest

Line

Tubercle

a small rounded projection, greater tubercle of humerus

Tuberosity

large, rounded projection, tibial tuberosity

Trochanter

very large projection, greater trochanter of femur

Spine

sharp slender projection, scapular spine

Epicondyle

projection located above a condyle, lateral epicondyle of femur

Crest

prominent, narrow, ridge-like projection, iliac crest

Line

ridge is less prominent than crest, linea asperea of femur

Cavities or depressions

Facet

Fossa

Notch

Foramen

Sinus

Sulcus

Facet

flattened or shallow articulating surface

ex: intervertebral facets in spine

Fossa

hollow, depressed or flattened surface

ex: glenoid fossa

Notch

depression in the margin of the bone

ex: radial notch of the ulna

Foramen

hole or opening in a bone

ex: obturator foramen

Sinus

cavity or hollow space within a bone

ex: frontal sinus

Sulcus

furrow or groove-like depression on a bone

ex: inter-tubercular (bicipital) groove of humerus

Compression

a squeezing force; bone is best able to withstand compressive forces

Tension

a pulling force

Shear

objects sliding across one another or moving in opposite directions

Torsion

a twisting force on bones

Longitudinal bone growth

occurs at epipiyseal plates

plates usually close around 18-20 years of age (females before males)

growth stops when lates close

Circumference of bone

growth of bone diameter continues throughout life

Osteoclasts

bone resorption of old, damaged bone

Osteoblasts

lay down new bone

Bone hypertrophy

increase in size as a result of stress

Bone atrophy

decrease in size when normal stresses exerted on bone by muscle or body weight are removed

ex: injury, bedrest

Wolff’s Law

• bone density increases in response to increased forces imposed

• bone density decreases in response to decreased forces imposed