The Axial Skeleton

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The Axial Skeleton part 2The Vertebral Column

• The spine or vertebral column
• protects the spinal cord
• supports the head and body

• 26 bones
• 24 vertebrae, the sacrum, and coccyx

• Regions
• Cervical (C) 7 v
• Thoracic (T) 12 v
• Lumbar (L) 5 v
• Sacral (S)
• Coccygeal (Co)

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• Curvatures
• Cervical curve
• Thoracic curve
• Lumbar curve
• Sacral curve

• Primary Curves
• Thoracic and sacral curves - present during fetal
  development
• aka accommodation curves-accommodate internal
  organs

• Secondary Curves
• Lumbar and cervical curves-appear after birth
• Aka compensation curves-shift body weight for
  upright posture

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Vertebrae

• 3 Parts of a Vertebra
• vertebral body (centrum)-transfers weight along
  the spine
• vertebral arch-posterior margin of vertebral
  foramen
• articular processes-lateral projections between
  laminae and pedicles

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• Intervertebral Discs
• Are pads of fibrocartilage
• Separate the vertebral bodies
• Absorb shocks

Figure 717d,e
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Vertebral Regions

• Vertebrae are numbered
• by region, from top to bottom
• C1 articulates with skull, L5 with sacrum
• Vertebrae of each region
• have characteristics determined by functions

Figure 716
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The Cervical Vertebrae

• Characteristics of C1C7
• small body (support only head)
• large vertebral foramen (largest part of spinal
  cord)
• C1 (atlas) has no spinous process all others have
  short spinous processes
• tip of each spinous process is notched (bifid)

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• Atlas (C1)
• articulates with occiptal condyles of skull
• has no body or spinous process
• has a large, round foramen within anterior and
  posterior arches

• Axis (C2)
• supports the atlas
• has heavy spinous process
• to attach muscles of head and neck
• Axis and atlas bodies fuse during development to
  form the dens

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• Vertebra prominens (C7)
• transitions to thoracic vertebrae
• has a long spinous process with a broad tubercle

• Whiplash
• a traumatic dislocation of cervical vertebrae

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The Thoracic Vertebrae

• Characteristics T1T12
• have heart-shaped bodies
• larger bodies than in C1C7
• smaller vertebral foramen than in C1C7
• long, slender spinous processes
• Dorsolateral surfaces of body have costal
  facets-which articulate with heads of ribs

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• T1T10
• Ribs at T1T10-contact costal and transverse
  costal facets

• T1T8 articulate with 2 pairs of ribs-at superior
  and inferior costal facets
• T9T11 articulate with 1 pair of ribs

• T10T12 transition to lumbar vertebrae

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The Lumbar Vertebrae

• Characteristics L1L5
• largest vertebrae
• oval-shaped bodies
• thicker bodies than T1T12
• no costal or transverse costal facets
• triangular vertebral foramen

• Transverse processes- slender
• Spinous process-short, heavy
• for attachment of lower back muscles

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Comparing Vertebrae
Table 72
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The Sacrum and Coccyx

• Characteristics - sacrum
• is curved, more in males than in females
• protects reproductive, urinary, and digestive
  organs
• attaches-the axial skeleton to pelvic girdle of
  appendicular skeleton
• broad muscles that move the thigh

• The adult sacrum
• consists of 5 fused sacral vertebrae
• fuses between puberty and ages 2530
• leaving transverse lines

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• Sacral canal
• replaces the vertebral canal

• Sacral cornua
• horn-shaped
• formed by laminae of the 5th sacral vertebra
• which do not meet at midline

• Sacral hiatus
• opening at the inferior end of the sacral canal
• formed by ridges of sacral cornua
• covered by connective tissues

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• Median sacral crest
• fused spinous processes

• Lateral sacral crest
• attach to muscles of lower back and hip

• Auricular surface
• articulates with pelvic girdle (sacroiliac joint)

• Sacral tuberosity
• attaches ligaments of the sacroiliac joint

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• 4 Regions of the Sacrum
• Base-the broad superior surface
• Ala-wings at either side of the base to attach
  muscles

• Sacral promontory-at the center of the base
• Apex-the narrow inferior portion articulates with
  the coccyx

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• Characteristics - coccyx
• attaches ligaments and a constricting muscle of
  the anus
• mature coccyx-consists of 3 to 5 fused coccygeal
  vertebrae

• first 2 coccygeal vertebrae-have transverse
  processes and have unfused vertebral arches
• coccygeal cornua-formed by laminae of 1st
  coccygeal vertebra

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The Thoracic Cage

• The skeleton of the chest-supports the thoracic
  cavity
• Consists of
• thoracic vertebrae
• ribs
• sternum (breastbone)

• Rib Cage - formed of ribs and sternum

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Articulations of Ribs and Vertebrae

• Functions
• Protects organs of the thoracic cavity-heart,
  lungs, and thymus

• Attaches muscles
• for respiration
• of the vertebral column
• of the pectoral girdle
• of the upper limbs

Figure 722b
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The Ribs

• Functions
• are flexible
• are mobile
• can absorb shock

• Rib movements (breathing)
• affect width and depth of thoracic cage
• changing its volume

• Ribs (costae)-12 pairs of long, curved, flat
  bones extending from the thoracic vertebrae

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• Ribs 17 (true ribs)
• vertebrosternal ribs
• connected to the sternum by costal cartilages

• Ribs 812 (false ribs)
• do not attach directly to the sternum

• Vertebrochondral ribs (ribs 810)
• fuse together
• merge with cartilage before reaching the sternum
• Floating or vertebral ribs (ribs 1112)
• connect only to the vertebrae
• have no connection with the sternum

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• Structures of the Ribs
• The head (capitulum)
• at the vertebral end of the rib
• has superior and inferior articular facets

• The neck
• the short area between the head and the tubercle

• The tubercle (tuberculum)
• a small dorsal elevation
• has an auricular facet that contacts the facet of
  its thoracic vertebra (at T1T10 only)

• The tubercular body (shaft)
• attaches muscles of the pectoral girdle and trunk
• attaches to the intercostal muscles which move
  the ribs

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The Sternum

• The sternum-a flat bone in the midline of the
  thoracic wall

• 3 parts
• 1-manubrium
• superior portion of sternum
• broad, triangular shape
• articulates with collarbones (clavicles)
  cartilages of 1st rib pair
• has a jugular notch between clavicular
  articulations

• 2-sternal body
• tongue-shaped
• attaches to the manubrium costal cartilages of
  ribs 27

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• 3-xiphoid process
• smallest part of the sternum
• attaches to the sternal body diaphragm and
  rectus abdominis muscles

• Development
• Sternum
• consists of 4 unfused bones
• completes fusion about age 25

• Xiphoid process
• last part of sternum to fuse
• can easily be broken away