Chapter 7

1. Chapter 7 Vertebral Column/Thoracic Cage

2. Vertebral Column • Location: • Forms the vertical axis of the skeleton • General Structure: • Composed of vertebrae • Vertenrae are separated by masses of fibrocartilage called intervertebral discs • Each intervertebral disc is connected to one another by ligaments • Functions: • Supports the head and trunk • Protects the spinal cord, which passes through the vertebral canal (formed by openings in the vertebrae)

3. Vertebral Column • Number of bones in an infant skeleton: • 33 bones • Number of bones in an adult skeleton: • 26 bones • Five bones are fused into the sacrum • Four bones are fused to form the coccyx (tailbone)

4. Vertebral Column • Curvatures: • Thoracic curvature • Concave anteriorly • Primary curve • Sacral curvature • Concave anteriorly • Primary curve • Cervical curvature • Convex anteriorly • Secondary curve • Develops when a baby begins to hold up its head • Lumbar curvature • Convex anteriorly • Secondary curvature • Develops when a child begins to stand

5. Typical Verterbra • Body • Drum-shaped • Forms the thick, anterior portion of the bone • Longitudinal rows of bodies support the weight of the head and trunk

6. Typical Vertebrae • Intervertebral discs • Separate adjacent vertebrae • Fastened to the roughened upper and lower surfaces of the vertebral bodies • Soften forces (such as from walking and jumping) that might fracture the vertebrae or injure the brain

7. Typical Vertebra • Anterior longitudinal ligaments • Join adjacent vertebrae on the anterior surface • Posterior longitudinal ligaments • Join adjacent vertebrae on the posterior surface

8. Typical Vertebrae • Vertebral Foramen • Opening through which the spinal cord passes

9. Typical Vertebrae • Vertebral Arch • Surrounds the vertebral foramen • Formed by: • Pedicles • Two short stalks that project posteriorly from each vertebral body to form the sides of the vertebral foramen • Spinous process • Posterior projection formed by the fusion of two plates called laminae • Serves as an attachment for various ligament sand muscles

10. Typical Vertebrae • Transverse process • Projects laterally and posteriorly between the pedicles and laminae • Serves as an attachment for various ligament sand muscles

11. Typical Vertebrae • Superior articulating process • Projects upward from each vertebral arch • Has cartilage-covered facets by which each vertebrae is joined to the one above it • Inferior articulating process • Projects downward from each vertebral arch • Has cartilage-covered facets by which each vertebrae is joined to the one above it

12. Typical Vertebrae • Intervertebral foramina • Formed by aligning notches on the lower surfaces of the vertebral pedicles • Provide passageways for spinal nerves that pass between adjacent vertebrae and connect to the spinal cord

13. Cervical Vertebrae • Seven vertebrae that form the neck • Smallest of the vertebrae • Have the densest bone tissues

14. Cervical Vertebrae • Special features: • Transverse processes have transverse foramina, which serve as passageways for arteries leading to the brain • Spinous processes of the 2nd through 6th cervical vertebrae are forked (bifid) to provide attachments for muscles • Spinous process of the 7th cervical vertebra is longer and called the vertebra prominens

15. Cervical Vertebrae • 1st cervical vertebra is called the atlas and supports the head • Hardly has a body or spine • Appears as a bony ring with two transverse processes • Has two kidney-shaped facets on its superior surface that articulate with the occipital condyles • 2nd cervical vertebra is called the axis • Has a toothlike process called the dens, or odontoid process that projects upward and into the ring of the atlas • As the head turns from side to side the atlas pivots around the dens

16. Thoracic Vertebrae • 12 vertebrae below the cervical vertebrae • Special features: • Transverse processes project posteriorly at sharp angles • Spinous processes are long and pointed and slope downward • Bodies have facets on each side that articulate with ribs • Beginning with the third thoracic vertebra, each vertebra increases in size to bear the increasing load of body weight

17. Lumbar Vertebrae • 5 vertebrae in the small of the back • Special Features • Have larger and stronger bodies than vertebrae above them as they have to support more weight • Have thinner transverse processes that project laterally • Have short thick spinous processes that project posteriorly and nearly horizontally

18. Sacrum • Consists of 5 vertebrae that gradually fuse together between the ages of 18 and 30 • Forms the posterior wall of the pelvic cavity

19. Sacrum • Special Features: • Spinous processes are fused to form a ridge of tubercules called the median sacral crest • Joined to the coxae of the pelvis at its auricular surfaces by fibrocartilage of the sacroiliac joints • The upper anterior margin of the sacrum (or the first sacral vertebra) is called the sacral promontory • Posterior sacral foramina are located to the sides of the tubercules and allow nerves and blood vessels to pass through • Vertebral foramina of the sacral vertebrae form the sacral canal which opens at the tip of the sacrum (called the sacral hiatus) • Opening exists because the laminae of the last sacral vertebrae are not fused • Four pairs of anterior sacral foramina are located on the ventral surface and allow passageways for nerves and blood vessels

20. Coccyx • Tailbone • Usually consists of 4 vertebrae that fuse by the 25th year. • Cushions the force of sitting • Attached to the margins of the sacral hiatus by ligaments

21. Thoracic Cage • Includes the ribs, the thoracic vertebrae, the sternum, and the costal cartilages (attach ribs to sternum) • Functions: • Support the shoulder girdle and upper limbs • Protect the viscera in the thoracic and abdominal cavities • Play a role in breathing

22. Ribs • Usual number is 24 (one pair attached to each of the 12 thoracic vertebrae) • Some people can develop extra ribs associated with the cervical or lumbar vertbrae • True ribs (vertebrosternal ribs) • First seven rib pairs • Join the sternum directly by costal cartilage • False ribs (vertebrochondral ribs) • Remaining five pairs • Cartilages of the upper three pairs of false ribs join the cartilage of the 7th rib • The last two pairs have no attachment to the sternum, so they are called floating ribs (or vertebral ribs)

23. Ribs • A typical rib has a long slender shaft which curves around the chest and slope downward • An enlarged head is located at the posterior end and articulates with a facet on the body of its own vertebra and the next highest vertebra • Neck of the rib is flattened, lateral to the head, where ligaments attach • A tubercle that is close to the head of the rib articulates with the transverse process of the vertebra

24. Ribs • Costal cartilages are composed of hyaline cartilage and are attached to the anterior ends of the ribs (and contour in line with them toward the sternum)

25. Sternum • Breastbone • Flat elongated bone located along the midline in the anterior portion of the thoracic cage • Develops in three parts: • An upper manubrium • The manubrium usually remains as a separate bone until middle age or later when it fuses to the body of the sternum • A middle body • A lower xyphiod process that projects downward • The xiphoid process begins as a piece of cartilage, slowly ossifies, and fuses to the body of the sternum by middle age • The sides of the manubrium and the body are notched where they articulate with costal cartilage • The manubrium also articulates with the clavicles by facets on its superior border