Skeletal System Axial Skeleton

AnatomyChapter 7

Skeletal SystemAxial Skeleton

axis- centerconsists of the center bones of the body80 bones

3 major regions:skullvertebral columnthoracic cage

Axial skeleton

most complex structuremostly flat boneshas about 85 named openings22 bones, usu interlocked along suture lines

8 cranium bones14 facial bones

Skull

helmetencloses and protects the brain, provides areas for muscle attachment for head movements and chewing

held together by sutures- immovable joints

Cranium

8 bones

1. frontal- forehead2. parietal- largest part (2)3. occipital-

external occipital protuberanceforamen magnumoccipital condyles

4. temporal (2)- Latin- temporum- time passing

external auditory meatusmastoid processstyloid process- (stake-like)zygomatic process

Frontal Occipital

Temporal

5. sphenoid- (spheno-wedge)helps form base of cranium, sides of skull, floors and sides of orbits; keystone

sella turcica- Turk’s saddle6. ethmoid bone- forms most of bony area of nasal cavity & eye orbits

cribiform platescrista galli- cock’s comb

Sphenoid

Facial bones14 bones- 13

immovable; 1 movable

Fxn: form basic shape of face, provide attachment for muscles, contain cavities for special sense organs, provide openings for air & food, & secure teeth

1. Maxillaekeystone bone of the face

form upper jaw, roof of mouth, floors of orbits and nasal cavity

Cleft palate

2. Zygomatic bonesform cheekbones

3. Mandiblehorseshoe shaped body

Sinusesfxn:

warm and humidify air

lighten skullenhance

resonance of voice

sinus infections

Fontanelsaka soft spotallows for movement through birth canal

close up by 2 years of age

Vertebral Column~ 28” long in adults

26 irregular bones adults

infants 33 bones

separated by intervertebral discs

Cervical VertebraeC1 – atlas

nod yes; up and down m’ment

C2- axisshake no; side to side m’ment

7 vertebrae

Thoracic VertebraeLarger than cervical

Articulate with ribs

12 vertebrae

Lumbar Vertebraebiggest vertebrae

bears most of body’s weight

small of back5 vertebrae

Sacrum and Coccyxsacrum- 5 fused vertebrae

form base of column

coccyx- lowest part of column

4 fused bones

Thoracic Cageincludes ribs,

thoracic vetebrae, sternum, costal cartilages

fxn: support pectoral girdle, protect viscera, aid in breathing

12 pairs (usually) join to a thoracic vertebra1st 7 ribs are TRUE RIBS- join sternum directly by their costal cartilages

next 5 pairs are FALSE RIBS- cartilage doesn’t reach sternum directly

next 2 (3) pairs are FLOATING RIBS- no cartilaginous attachment to sternum

Ribs

usu break at greatest curvature

middle ribs commonly fractured

Sternumaka breastbone~ 6” longxyphoid process doesn’t completely ossify until about 40 years old

Hyoid BoneOnly bone in body that doesn’t articulate w/ other bones

Enables us to talk

Smallest bones of body

Spongy & Compact bone

process of bone developingbones form by replacing existing connective tissue in either of 2 ways:

1. intramembranous ossification- formation of bone directly on or within fibrous membranes

Ossification

simplest, most direct type of bone development

osteoblasts form bone tissueskull & clavicles formed this way

replacement of hyaline cartilage shapes by bone tissue

endo= within chondro= cartilage

2. endochondral ossification

growth takes place at the epiphyseal plates on the long bones

most bones of body form this waymore complex methodby age 25 all bones are ossifiedclavicle- last bone to stop growing

bone REMODELING occurs continuously thru-out life

Male vs FemaleSkull: mastoid process, size of skull, forehead, weight

Limbs

Pelvic cavity: wider in females, pubic arch > 90o

aka articulationbind parts of skeletal systemmake bone growth possibleallow parts of skeleton to change

shape during childbirthenable body to move during muscle

contraction

230 joints in body

Joints

3 classifications:immovableslightly movablefreely movable

Fibrousbasically NO movement

bones lie in close contact w/ each other

ex: sutures in skull

Cartilaginoushyaline cartilage connects bones

slightly movable

Synovial Jointsfreely movablesynovial fluid

reduces frictionjoint capsulemenisci-bursae6 types

Ball and Socketwider range of motion

hipshoulder

Condyloidcondyle fits into elliptical cavity

variety of m’ments in different planes; rotational m’ment not allowed

Gliding Joint (plane)most joints in wrists & ankles

allow sliding & twisting motion

Pivot jointscylindrical bone rotates

rotation around central axis

Hinge jointallows for flexion and extension

Saddle Jointvariety of m’ment