Axial Skeleton

*I can name and identify all of the bones of the axial skeleton.

*I can describe the major landmarks of the cranial and facial bones

*I can describe and discuss the differences between the cervical, thoracic, lumbar, sacral and coccygeal vertebrae

I. Axial skeleton

A.The axial skeleton forms the central axis of the body.

1. made up of:

a. skull

b. vertebral column

c. ribs

d. sternum

2. functions: supports & protects brain, provides surface area for muscle attachment

Section 2

B. Skull

1. can be divided into two categories

a. cranium - enclosed brain

b. facial bones

2. Cranial bones: 8 cranial bones form case to protect & contain brain

a. Frontal bone - single convex bone -extends from orbits to the coronal suture

- forms forehead & roof of the eye orbits

-Frontal sinuses: air filled cavities, lie within the frontal bone

b. Occiptal bone- forms back bottom part - foramen magnum: opening in occipital bone, connects cranium to spinal cavity -Occipital condyles mark articulation w/ vertebra of neck

c. Parietal bones (2)- form middle top portion

d. Temporal Bones (2)- form lower sides, temple region

-zygomatic process helps form cheek bone - external acoustic meatus- opening to outer ear - mastoid process: attachment site for muscles that rotate or extend the head - styloid process: attachment site of tendons of muscles associated w/ tongue

e. Sphenoid- forms part of the floor of the

cranium (inside top)-looks like bat w/ wings extended

-great wing: form back wall of eye orbit -pterygoid process: attachment sites for

muscles that move jaw

f. Ethmoid-inside, top, forms roof of nasal cavity-cribriform plate: forms floor of cranium- perpendicular plate: forms part of nasal septum

3. sutures- immovable joints that form between bones of the skull (pg 215)

a. lamboid- btwn occipital & parietal bonesb. coronal- btwn frontal & parietal bonesc. sagittal- btwn 2 parietal bonesd. squamous- btwn temporal & parietal (on R & L sides)

4. Facial bones

a. Maxillae (2)- support upper teeth, form upper jaw, inferior orbital rim, & most of hard palate

b. Palatine bones (2)- form posterior portion of hard palate & bottom of orbit

c. Nasal bones (2)- supper bridge of nose

d. Vomer (1) – forms inferior part of nasal septum

e. Inferior nasal conchae (2)- inside nasal cavity, help increase epithelial surface area to warm humidify air

f. Lacrimal bones (2)- smallest facial bone, forms medial part of eye orbit

g. Mandible (1)- forms the lower jaw, alveolar processes support teeth, condylar process articulates with the temporal bone (tmj- temporal mandibular joint)

C. Foramina & Fissures of Skull

1. allow passageway for nerves and blood vessels in skull

a. examples: *supra-orbital foramen: nerve and blood vessel supply to eyebrow/eyelid

* optic canal in sphenoid- optic nerve brings info from eye to brain

D. Orbital & Nasal complexes

1. orbits- bony recesses that contain eyes

a. orbit is formed by 7 bones of orbital complex

b. frontal bone forms most of roof; maxilla most of the floor

c. lacrimal, ethmoid, sphenoid, zygomatic bone, & palatine bone help make up orbit as well

E. Fontanelles

1. largest fibrous areas btwn cranial bones

2. at birth, cranial bones are connected by fibrous connective tissue- allow distortion of skull (delivery)

3. anterior fontanelle is the largest- where frontal, sagittal, & coronal sutures meet

a. known as soft spot

b. present until nearly 2 yrs of age!

4. occipital, sphenoidal, & mastoid fontanelles disappear w/in 1-2 months after birth

5. growth of cranium is coordinated w/ expansion of brain- brain stops growing before age 5, cranial sutures develop

F. Vertebral column

1. spine has 26 bones: 24 vertebrae, sacrum, 1 coccyx (tailbone)

2. functions

a. provides support for head, neck & trunk

b. protects spinal cord

3. structure- four curves- help bring body weight in line with body axis

a. cervical, thoracic, lumbar, & sacral

b. primary curves- curves in infants- C shape from thoracic & sacral curves

c. secondary curves- lumbar & cervical, form months after birth

4. vertebra- three basic parts

a. body- transfers weight along vertebral column, separated by cartilage (intervertebral discs)

b. arch- forms part of vertebral foramen

-has walls (pedicles)

- roof (lamina)

- forms vertebral canal, which encloses the spinal cord

c. articular processes

- spinous process is located where laminae fuse, projects out (you see/feel these)

- transverse processes project laterally; sites of muscle attachment or rib articulation

-articular processes: superior & inferior: where each vertebra articulates with the one above & below it

d. intervertebral foramina- gaps btwn pedicles of successive vertebrae, allow passage of nerves running to/from spinal cord

G. Regions of the vertebrae

* cervical (1-7): neck

* thoracic ( 1-12): superior portion of back

* lumbar (1-5): inferior portion of back

* sacrum (fused)

* coccyx (fused)- tailbone

1. cervical vertebrae

a. most mammals have 7

b. smallest in vertebra column- small body, large vertebral foramen

c. head is large in comparison- rapid change is speed can cause whiplash, partial or complete dislocation of cervical vertebrae

d. C1 is called the Atlas

* holds up head, articulates w/occipital condyles

*permits you to nod “yes”

*doesn’t have a body or a spinous process

* large round vertebral foramen

e. C2 is called the Axis

* fused to atlas, creating the dens- a process on the axis, allows you to shake “no”

*fusion is not complete in children- shaking can cause damage to spinal cord

f. c7 is the vertebra prominens

* last cervical vertebra

* large transverse processes for muscle attachment

* ligamentum nuchae- ligament begins at c7 and extends to occipital crest-helps you lift your head

2. Thoracic vertebrae

*12 total, heart shaped body that is larger than cervical

*smaller vertebral foramen

*each articulates w/ ribs at costal facets of vertebrae

* T1-T8 each articulate w/ 2 pair of ribs, have superior and inferior sets of facets

* T9-T11 articulate w/ one pair- single set of facets

3. Lumbar vertebrae

* 5 total, largest of vertebrae, have thicker body

* don’t have costal facets

*transverse process stick out (most like a “t”)

*bear the most weight, massive spinous processes provide area for attachment of lower back muscles

4. Sacrum- five fused sacral vertebrae

* vertebrae begin fusing after puberty & are fused by age 25-30

* protects reproductive, digestive, & urinary organs

* attaches axial skeleton to pelvic girdle

* crests – ridges that form where process of individual vertebrae fused

* base- superior portion, apex- narrow inferior portion, ala- (wing)- extends on either side

5. coccyx- small, consists of 3-5 vertebrae, fused by age 26

* provides attachment site for ligaments & a muscle associated w/ anal opening

* coccygeal cornua- stick out of 1st vertebrae, curve to meet sacrum

H. Thoracic Cage- chest

1. consists of : thoracic vertebrae, ribs, & sternum

2. functions include:

a. protection of heart, lungs, thymus

b. attachment site for muscles involved in respiration, maintaining position of spine, & movements of pectoral girdle & upper limbs

3. Ribs (costae)

a. elongate, flattened bones

b. 12 pairs

c. true ribs- 1st-7th pair, are connected to sternum by costal cartilages

d. false ribs- 8th -12th pairs, don’t attach directly to sternum, but fuse together

e. 11th & 12th pair- floating ribs, no connection w/ sternum

f. Parts of Ribs

- head (capitulum)- end that articulates w/ vertebra

- tuberculum- contacts transverse process of vertebra

- long shaft is the body

g. ribs can bend/move to absorb blows, sudden impact can result in fracture

h. ribs are bound tightly in CT, so can heal w/o cast

4. Sternum- breastbone

a. three parts

* manubrium- widest, most superior part, has jugular notch btwn clavicle

articulations

* body- where ribs 2-7 attach to sternum

* xiphoid process- smallest, inferior part, diaphragm & rectus abdominis

muscles attach, easily broken by impact

b. ossification of sternum- age 6-10, not complete until age 25 (before fusion, body alone is 4

separate bones)