The Axial Skeleton

Chapter 7

I. Skeletal Divisions (206 bones)

A. Axial Skeleton (80 bones)1. Forms longitudinal axis of the body

2. Consists of:Skull

Vertebral column

Ribs

Sternum

B. Appendicular Skeleton (126 bones)1. Consists of

a. Pectoral girdle

b. Pelvic girdle

c. Bones of the limbs

II. The Skull (22 bones)

A. Functions1. Protects

2. Guards entrances to digestive & respiratory systems

B. Cranium (braincase) (8 bones)

1. Occipital Bone (1 bone)

Forms posterior & inferior surfaces

2. Parietal Bones (2 bones)

Forms superior & lateral surfaces

3. Frontal Bone (1 bone)

Forms anterior portion of skull & roof of orbits

4. Temporal Bones (2 bones)

Surrounds & protects sense organs of inner ear

5. Sphenoid Bone (1 bone)

Cross-brace that strengthens sides of skull (looks like a bat)

6. Ethmoid Bone (1 bone)

Forms roof of nasal cavity, part of nasal septum

C. Facial Bones ( 14 bones)

1. Maxillary Bones (2 bones)

Supports the teeth

2. Palatine Bones (2 bones)

Forms portion of hard palate

3. Lacrimal Bones (2 bones)

Forms medial wall of orbits

4. Nasal Bones (2 bones)

Supports superior portion of bridge of nose

5. Zygomatic Bones (2 bones)

Forms rim & lateral wall of orbits

6. Vomer Bone (1 bone)

Forms interior portion of bony nasal septum

7. Inferior Nasal Conchae (2 bones)

Creates turbulence in air passing through nasal cavity

WHY???

8. Mandible Bone (1 bone)

Lower jaw

D. Sinuses1. Makes bones lighter

2. Produces mucus to moisten & clean air in and near the sinuses

E. Sutures- Immovable joints connected with dense fibrous connective tissue

1. Lambdoidal Suture- between occipital & parietal bones

2. Coronal Suture- between frontal and parietal bones

3. Sagittal Suture- between parietal bones

4. Squamosal Sutures- between temporal & parietal bones

5. Fontanels- fibrous area between cranial bones in infants

a. allow skull to be distorted/squished to ease delivery

b. the frontal fontanel persists until a child is nearly 2 yrs. old

Sutures of the Skull

F. Associated Bones of the Skull (7)

1. Auditory Ossicles (6 bones)a. 3 bones per ear

b. malleus, incus & staples

1. Hyoid Bone (1 bone)a. Supports larynx

b. Only free standing bone not connected to another bone

III. The Vertebral Column

- 33 total bones

A. Functions of the V.C.

1. Provide a column of support

2. Bear the weight of the head, neck & trunk

2. Protect the spinal cord

3. Helps maintain an upright body position

(Sitting/Standing)

B. Divisions of the V.C.

1. Cervical Regiona) Made of 7 vertebrae b) Constitutes the neck region

c) Labeled C1-C7 (Superior to Inferior)

i. C1 is called the Atlas-holds up the head- Articulates w/ occipital condyles- Allows “yes” movement

ii. C2 is called the Axis- Pivots around the Atlas- Allows “no” movement

2. Thoracic Region

a) Made of 12 vertebrae

b) Constitutes the chest/upper back region

c) Labeled T1-T12 (Superior to Inferior)

d) Articulate with the ribs

3. Lumbar Region

a) Made of 5 vertebrae

b) Constitutes the lower back region

c) Labeled L1-L5 (Superior to Inferior)

d) Large, weight-bearing bones

e) Provides site for muscle attachment

4. Sacrum

a) Made of 5 fused vertebrae

b) Constitutes the posterior portion of the pelvis

c) Provides protection for reproductive, digestive, & urinary organs

5. Coccyx

a) Made of 3-5 fused vertebrae

b) Also known as the tailbone

5 Divisions of the V.C.

Cervical

Thoracic

Lumbar

Sacrum

Coccyx

C. Spinal Curvatures

1) Thoracic Curvature

2) Sacral Curvature

- 1) & 2) are known as Primary or Accommodation curves b/c they

appear in fetal development

3) Cervical Curvature

4) Lumbar Curvature

- 3) & 4) are known as Compensation curves b/c they develop as we

learn to walk (help shift weight over legs)

4 Spinal Curvatures

IV. The Thoracic Cage

A. Consists of the thoracic vertebrae, ribs, & sternum

B. Functions

1) Protects the heart, lungs, thymus & other structures

2) Serves as an attachment point for muscles

C. The Ribs

1. 12 pair of curved, flat bones

2. Originate on or between thoracic vertebrae

3. End in the wall of the thoracic cavity

D. Kinds of Ribs

1) True/Vertebrosternal Ribs

a) First 7 pairs, most superior

b) Connected to sternum by cartilaginous extensions

2) False/Vertebrochondral Ribs

a) Ribs 8-12

b) The cartilage on the ends of these ribs fuse together with rib 7

3) Floating Ribs

a) Last 2 pairs (11th & 12th)

b) Not connected to sternum at all

E. The Sternum (breastbone)

1. Flat bone

2. Forms the anterior midline of the thoracic wall

F. Divisions of the Sternum

1) Manubrium

a) Most superior part of the sternum

b) Triangular shaped

c) Articulates w/ the clavicles & the cartilage of the 1st pairs of ribs

2) Body

a) Tongue shaped

b) Costal Cartilage from pairs 2-7 attach here

3) Xiphoid Process

a) Most inferior part of sternum

b) Smallest part of sternum

c) The diaphragm & some abdominal muscles attach here

The Thoracic Cage