The Axial Skeleton

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The Axial Skeleton

• Chapter 7

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I. Skeletal Divisions (206 bones)

• Axial Skeleton (80 bones)
• Forms longitudinal axis of the body
• Consists of
• Skull
• Vertebral column
• Ribs
• Sternum

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• Appendicular Skeleton (126 bones)
• Consists of
• Pectoral girdle
• Pelvic girdle
• Bones of the limbs

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II. The Skull (22 bones)

• Functions
• Protects
• Guards entrances to digestive respiratory
  systems

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1. Cranium (braincase) (8 bones)

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1. Occipital Bone (1 bone)

• Forms posterior inferior surfaces

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2. Parietal Bones (2 bones)

• Forms superior lateral surfaces

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3. Frontal Bone (1 bone)

• Forms anterior portion of skull roof of orbits

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4. Temporal Bones (2 bones)

• Surrounds protects sense organs of inner ear

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5. Sphenoid Bone (1 bone)

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

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6. Ethmoid Bone (1 bone)

• Forms roof of nasal cavity, part of nasal septum

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1. Facial Bones ( 14 bones)

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1. Maxillary Bones (2 bones)

• Supports the teeth

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2. Palatine Bones (2 bones)

• Forms portion of hard palate

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3. Lacrimal Bones (2 bones)

• Forms medial wall of orbits

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4. Nasal Bones (2 bones)

• Supports superior portion of bridge of nose

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5. Zygomatic Bones (2 bones)

• Forms rim lateral wall of orbits

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6. Vomer Bone (1 bone)

• Forms interior portion of bony nasal septum

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7. Inferior Nasal Conchae (2 bones)

• Creates turbulence in air passing through nasal
  cavity
• WHY???

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8. Mandible Bone (1 bone)

• Lower jaw

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• Sinuses
• Makes bones lighter
• Produces mucus to moisten clean air in and near
  the sinuses

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• E. Sutures- Immovable joints connected with dense
  fibrous connective tissue
• Lambdoidal Suture- between occipital parietal
  bones
• Coronal Suture- between frontal and parietal
  bones
• Sagittal Suture- between parietal bones

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• 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

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Sutures of the Skull
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F. Associated Bones of the Skull (7)

• Auditory Ossicles (6 bones)
• 3 bones per ear
• malleus, incus staples

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• Hyoid Bone (1 bone)
• Supports larynx
• Only free standing bone not connected to another
  bone

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III. The Vertebral Column

• - 33 total bones

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A. Functions of the V.C.

• Provide a column of support
• Bear the weight of the head, neck trunk
• Protect the spinal cord
• Helps maintain an upright body position
• (Sitting/Standing)

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B. Divisions of the V.C.

• Cervical Region
• a) 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

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• 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

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• 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

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• 4. Sacrum
• a) Made of 5 fused vertebrae
• b) Constitutes the posterior portion of the
  pelvis
• c) Provides protection for reproductive,
  digestive, urinary organs

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• 5. Coccyx
• a) Made of 3-5 fused vertebrae
• b) Also known as the tailbone

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5 Divisions of the V.C.
Cervical Thoracic Lumbar Sacrum Coccyx
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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

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• 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)

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4 Spinal Curvatures
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IV. The Thoracic Cage

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

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B. Functions

1. Protects the heart, lungs, thymus other
   structures
2. Serves as an attachment point for muscles

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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

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D. Kinds of Ribs

• True/Vertebrosternal Ribs
• a) First 7 pairs, most superior
• b) Connected to sternum by cartilaginous
  extensions

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• False/Vertebrochondral Ribs
• a) Ribs 8-12
• b) The cartilage on the ends of these ribs fuse
  together with rib 7

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• 3) Floating Ribs
• a) Last 2 pairs (11th 12th)
• b) Not connected to sternum at all

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E. The Sternum (breastbone)

1. Flat bone
2. Forms the anterior midline of the thoracic wall

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F. Divisions of the Sternum

• Manubrium
• a) Most superior part of the sternum
• b) Triangular shaped
• c) Articulates w/ the clavicles the cartilage
  of the 1st pairs of ribs

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• Body
• a) Tongue shaped
• b) Costal Cartilage from pairs 2-7 attach here

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• Xiphoid Process
• a) Most inferior part of sternum
• b) Smallest part of sternum
• c) The diaphragm some abdominal muscles
  attach here

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The Thoracic Cage