Skeletal System: The Axial Skeleton

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Skeletal SystemThe Axial Skeleton

• SkullVertebral Column
• Ribs
• Sternum

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The Skull

• 22 separate bones, many fused together
• Two divisions
• Cranial Bones (8 bones)
• Facial Bones (14 bones)

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Bones of the Cranium

• Enclose and protect the brain
• Bones
• Frontal (1)
• Parietal (2)
• Temporal (2)
• Occipital (1)
• Sphenoid (1)
• Ethmoid (1)

Sphenoid bone
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Ethmoid and Sphenoid Bones

• Ethmoid Bone anterior part of the cranium base
• Forms the floor of the cranium
• Makes up the medial wall of the orbits (eye
  sockets)
• The major supporting structure for the nasal
  cavity
• Sphenoid Bone medial base of the skull
• Connects the frontal, temporal, and parietal
  bones
• Sella Turcica a saddle for the pituitary gland
  in the brain

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Sutures in the Skull

• Suture An immovable joint found only in the
  skull bones
• Coronal Suture between the frontal and two
  parietals
• Sagittal Suture between the two parietals
• Lambdoid Suture between the two parietals and
  the occipital
• Squamous Sutures between the parietals and
  temporal bones

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Fontanels

• Membrane-filled spaces found between cranium
  bones in infants
• Soft Spots
• Eventually become ossified (replaced by bone)
• Allow for
• The babies skull to compress, thus allowing
  childbirth
• The brain to grow before the skull is completely
  fused

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Facial Bones

• Your face grows the most in the first two years
  then stops by the age of 16.
• Nasal Bones
• Maxillae form the lower orbit and upper jaw
• Zygomatic Bones cheekbones
• Mandible lower jawbone
• Lacrimal Bones smallest bones in the face have
  a foramen for the tear duct to pass
• Palatine Bones form the hard palate in the roof
  of the mouth

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Hyoid Bone

• A U-shaped bone located in the neck between the
  mandible and the larynx (voicebox)
• Does not articulate with any other bone
• Supports the tongue
• Provides attachment for muscles to allow for neck
  movement and swallowing

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Vertebral Column

• Protects the Spinal Cord
• Allows the major nerves to enter and exit the
  spinal cord
• Usually 33 Bones
• 7 Cervical
• 12 Thoracic
• 5 Lumbar
• 5 Sacral (fused to form the sacrum)
• 4 Coccygeal (fuse to form one or two fused
  coccyx)

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Typical Vertebra

• Body the thick weight bearing portion
• Vertebral foramen the hole that holds the
  spinal cord
• Spinous Process a single projection for muscle
  attachment
• Transverse Process two lateral projections for
  muscle attachment
• Articular Processes the facets that allow the
  vertebrae to move with the vertebrae superior and
  inferior to them

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Atlas and Axis

• Atlas (C1) supports the head
• Articulates with the occipital condyles of the
  skull (nod your head yes)
• Axis (C2) The peglike dens makes a pivot for
  the head to rotate (move your head no)

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Sacrum and Coccyx

• Sacrum (holy bone) 5 fused vertebrae
• Usually starts to fuse at age 16-18 and end in
  mid 20s)
• Provides a foundation for the pelvis and allows
  nerves to pass
• Coccyx Usually 4 vertebrae that fuse
• Fusion occurs between 20-30 years of age

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Epidural Anesthesia
Numbing medicine is delivered near the spinal
cordthrough the sacrum
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Sternum

• Aka Breastbone
• Three separate bones
• Manubrium
• Body
• Xiphoid Process
• Articulates with the ribs, provides attachment
  point for some abdominal muscles, hemopoiesis
• Fuses in late teens completely by age 40.

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Ribs

• 12 pairs (24 total)
• True Ribs pairs 1-7 directly attach to the
  sternum by costal cartilage
• False Ribs pairs 8-12, their cartilage attaches
  to the 7th rib cartilage
• Floating Ribs pairs 11-12 dont attach to the
  sternum