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Skeletal System
Axial Skeleton

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Pre-Quiz
Types of Skeletons
Joints
Skeletal Functions
Types of Bones
Structure of Long Bones
Microscopic Structure
Skeletal Development
Axial Skeleton
Appendicular Skeleton
Interactive Skeleton
Diseases, Disorders and Fractures
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Post-Quiz

The Axial skeleton is composed of the skull, bony thorax and vertebral column.  It contains a total of 80 bones, out of the bodies 206.

Skull
   Composed of:     
          - 8 cranial bones
          - 14 facial bones
          - 6 tiny bones forming the ear
    Sinuses are spaces or cavities within some cranial bones.  Four pairs  are referred to as the paranasal sinuses because they have opening into the nose.  Sinusitis occurs when the mucus membrane that lines them becomes inflamed, swollen and painful.
    Sutures are the synarthrotic (immovable) joints connecting the individual cranial bones to one another.
    Fontanels are the soft spots on a baby's skull.  They are actually areas of incomplete ossification which allow for compression during childbirth.  They disapear within 2 years, and their pulse can actually be felt on these areas. 

labeledskull.gif

Vertebral Column
    Composed of:
        - 26 irregular bones
          - 7  Cervical Vertebrae - includes atlas and axis (top two)
          - 12  Thoracic Vertebrae - larger than cervical, connect to ribs
          - 5  Lumbar Vertebrae - bulky and sturdy, carry weight, larger than thoracic
 
     Vertebrae are seperated by pads of flexible fibrocartilage called intervertebral disks that cushion and absorb shocks.  As a person ages the water content of the disks decreases making them less spongy and compressible.
      Spine is S shaped for flexibility and to absorb shock.  The thoracic and sacral regions contain primary curvatures (present at birth) whereas the cervical and lumbar regions contain secondary curvatures (develop when baby lifts its head and walks).

vertebralcolumn.jpg
Key: Purple-Cervical Vertebrae, Dark Blue - Thoracic V., Light Blue - Lumbar V.

Bony Thorax
    Composed of:
         - Sternum & Xiphoid process
         - Ribs:
            - 12 pairs total, 7 are true ribs (connect to sternum via costal cartilage)
                                    5 are false ribs (connect indirectly via cartilage or not at all)
                                    2 pairs of false ribs are 'floating ribs' which do not connect to the sternum
      The bony thorax ( or thoracic cage) forms a protective cone-shaped cage of slender bones around the organs of the thoracic cavity.

thorax.jpg