A J

Sacrum

Coccyx

Thoracic vertebrae

Lumbar vertebrae

Sacrum

Figure 7.34

The curved vertebral column consists of many vertebrae separated by intervertebral disks. (a) Left lateral view. (b) Posterior view.

are concave anteriorly and are called primary curves. The cervical curvature in the neck and the lumbar curvature in the lower back are convex anteriorly and are called secondary curves. The cervical curvature develops when a baby begins to hold up its head, and the lumbar curvature develops when the child begins to stand.

A Typical Vertebra

Although the vertebrae in different regions of the vertebral column have special characteristics, they also have features in common. A typical vertebra (fig. 7.35) has a drum-shaped body, which forms the thick, anterior portion of the bone. A longitudinal row of these vertebral bodies sup ports the weight of the head and trunk. The intervertebral disks, which separate adjacent vertebrae, are fastened to the roughened upper and lower surfaces of the vertebral bodies. These disks cushion and soften the forces caused by such movements as walking and jumping, which might otherwise fracture vertebrae or jar the brain. The bodies of adjacent vertebrae are joined on their anterior surfaces by anterior longitudinal ligaments and on their posterior surfaces by posterior longitudinal ligaments.

Projecting posteriorly from each vertebral body are two short stalks called pedicles (ped'i-k'lz). They form the sides of the vertebral foramen. Two plates called laminae (lam'i-ne) arise from the pedicles and fuse in the back to become a spinous process. The pedicles, laminae, and spinous process together complete a bony vertebral arch around the vertebral foramen, through which the spinal cord passes.

Between the pedicles and laminae of a typical vertebra is a transverse process, which projects laterally and posteriorly. Various ligaments and muscles are attached to the dorsal spinous process and the transverse processes. Projecting upward and downward from each vertebral arch are superior and inferior articulating processes. These processes bear cartilage-covered facets by which each vertebra is joined to the one above and the one below it.

On the lower surfaces of the vertebral pedicles are notches that align to help form openings called intervertebral foramina (in"ter-ver'te-bral fo-ram'i-nah). These openings provide passageways for spinal nerves that proceed between adjacent vertebrae and connect to the spinal cord.

through the sixth cervical vertebrae are uniquely forked (bifid). These processes provide attachments for muscles.

The spinous process of the seventh vertebra is longer and protrudes beyond the other cervical spines. It is called the vertebra prominens, and because it can be felt through the skin, it is a useful landmark for locating other vertebral parts (see fig. 7.34).

Two of the cervical vertebrae, shown in figure 7.36, are of special interest. The first vertebra, or atlas (at'las), supports the head. It has practically no body or spine and appears as a bony ring with two transverse processes. On its superior surface, the atlas has two kidney-shaped facets, which articulate with the occipital condyles.

The second cervical vertebra, or axis (ak'sis), bears a toothlike dens (odontoid process) on its body. This process projects upward and lies in the ring of the atlas. As the head is turned from side to side, the atlas pivots around the dens (figs. 7.36 and 7.37).

Thoracic Vertebrae

The twelve thoracic vertebrae are larger than those in the cervical region. Each vertebra has a long, pointed spi-nous process, which slopes downward, and facets on the sides of its body, which articulate with a rib.

Beginning with the third thoracic vertebra and moving inferiorly, the bodies of these bones increase in size. Thus, they are adapted to bear increasing loads of body weight.

Lumbar Vertebrae

The five lumbar vertebrae in the small of the back (loins) support more weight than the superior vertebrae and have larger and stronger bodies. Compared to other types of vertebrae, the transverse processes of these vertebrae project posteriorly at sharp angles, whereas their short, thick spinous processes are nearly horizontal. Figure 7.38 compares the structures of the cervical, thoracic, and lumbar vertebrae.

Gymnasts, high jumpers, pole vaulters, and other athletes who hyperextend and rotate their vertebral columns and stress them with impact sometimes fracture the portion of the vertebra between the superior and inferior articulating processes (the pars interarticu-laris). Such damage to the vertebra is called spondylolysis, and it is most common at L5.

Cervical Vertebrae

Seven cervical vertebrae comprise the bony axis of the neck. These are the smallest of the vertebrae, but their bone tissues are denser than those in any other region of the vertebral column.

The transverse processes of the cervical vertebrae are distinctive because they have transverse foramina, which are passageways for arteries leading to the brain. Also, the spinous processes of the second

The painful condition of spondylolisthesis occurs when a vertebra slips out of place over the vertebra below it. Most commonly the fifth lumbar vertebra slides forward over the body of the sacrum. Persons with spondylolysis (see previous box) may be more likely to develop spondylolisthesis, as are gymnasts, football players, and others who flex or extend their vertebral columns excessively and forcefully.

Superior articulating process

Transverse process

Inferior articulating process

Spinous process

Superior articulating process

Transverse process

Facet for tubercle of rib

Body

Body

Superior articulating process

Transverse process

Inferior articulating process

Spinous process

Anterior

Posterior

Pedicle Vessles

Pedicle

Body

Intervertebral notch

Inferior articulating process

Spinous process

Spinous process

Intervertebral disk

Anterior

Posterior

Intervertebral disk

Spinous process Lamina

Transverse process

Superior articulating process Vertebral foramen Pedicle

Body

Pedicle

Body

Intervertebral notch

Inferior articulating process

Spinous process Lamina

Transverse process

Superior articulating process Vertebral foramen Pedicle

Body

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