The Axial Skeleton

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The Axial Skeleton
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Human Skeleton

• Triumph in design
• Strong yet light
• Perfectly adapted for protective, locomotor and
  manipulative functions
• 20 of body mass
• Consists of axial and appendicular portions

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Axial Skeleton

• Consists of skull, vertebral column and bony
  thorax
• 80 bones total

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Skull

• Most complex bony structure
• Consists of cranial and facial bones
• 22 bones in all

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Cranial Bones

• 8 total, together form brains protective
  helmet
• Enclose and protect brain
• Site for head and neck muscle attachment
• Consists of the following
• Parietal Pair
• Temporal Pair
• Frontal
• Occipital
• Sphenoid
• Ethmoid

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Facial Bones

• Form framework of the face
• Contain cavities for sense organs
• Provide openings for passage of air and food
• Secure the teeth
• Anchor the facial muscles of expression

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Sutures

• Most skull bones are flat bones
• United by interlocking joints, sutures
• Coronal
• Sagittal
• Squamous
• Lambdoid

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Vertebral Column

• Formed from 26 irregular bones connected so that
  a flexible, curved structure results
• Extends from the skull to the pelvis
• Surrounds and protects the delicate spinal cord
• Provides attachment points for the ribs and
  muscles of the back and neck

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Divisions of Vertebral Column

• Cervical Vertebrae 7 vertebrae of the neck
• Thoracic Vertebrae the next 12
• Lumbar Vertebrae 5 supporting the lower back
• Sacrum 5 fused vertebrae
• Coccyx 4 fused vertebrae
• (See Figure 7.13)

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General Structure of Vertebrae

• Centrum (body)- anterior
• Vertebral arch- posterior
• Pedicles- pillars coming off body
• Laminae- flattened plates that complete the arch
• Spinous process- projection at junction of two
  laminae
• Transverse process- projection, lateral from each
  side
• Vertebral canal- spinal cord passes through
• See figure 7.15

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Atlas and Axis

• First two cervical vertebrae
• No intervertebral disc
• Atlas no body or spinous processes
• Anterior and posterior arches
• Lateral arch
• Carries the skull
• Axis like other vertebrae, but also has a dens
  (odontoid process), which fuses with the atlas
• See Figure 7.16

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Characteristics of Regional Vertebrae

• Note Table 7.2 to differentiate structure and
  function for each type of vertebrae

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The Bony Thorax

• AKA Thoracic Cage
• Includes thoracic vertebrae, ribs, costal
  cartilages and sternum

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Functions of Thoracic Cage

• Forms a protective cage around vital organs of
  thoracic cavity
• Supports shoulder girdles and upper limbs
• Provides attachment points for muscles of neck,
  back, chest and shoulders

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Sternum

• 15 cm long
• Fusion of three bones
• Manubrium (superior portion)
• Body (bulk)
• Xyphoid process (inferior end)

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Ribs

• Twelve pairs
• Attach posteriorly to thoracic vertebrae
• Superior 7 pairs of ribs attach directly to
  sternum by individual costal cartilage (hyaline)
• True (vertebrosternal) ribs
• Remaining 5 pairs of ribs attach indirectly to
  sternum or not at all
• False (vertebrochondral) ribs
• 8-10 attach to costal cartilage immediately above
• 11-12 floating ribs, costal cartilage embedded
  in muscles of lateral body wall