What are They?

Remember Anatomy 101, the white bony structure dangling in the lab, and the professor's lecture on the spinal column? If you went to sleep because it was too complex, we're here to make it easier for you. While you snored through it, the professor probed the odd-shaped bones with a pointer, explaining that the spine was an interlocking structure of peculiar-looking bones called vertebrae. Very interesting, right? But what are vertebrae? Vertebrae are the building blocks of your spine (see figure to the left). The twenty-four separate vertebrae are spool shaped and about an inch in height. They protect ten billion nerve cells in the spinal cord. Stacked between each vertebra is a shock absorbing disk. If we put too much pressure on a disk, it can rupture, or herniate , and may be extremely painful. This vertebrae-disk combination originally supported animals that walked on all fours. Evolution changed all that.

The vertebrae, which is pronounced ver´ tê bray, singular ver´tê-brah, are any of the separate segments comprising the spine or vertebral column. The vertebrae support the body and provide the protective bony corridor through which the spinal cord passes.

The weight-bearing portion of a typical vertebra is called the vertebral body, the most forward portion. (see image on right). This is a cylindrical structure that is separated from the vertebral bodies above and below by disks of cartilage and fibrous tissue. These intervertebral disks act as cushions to absorb the mechanical shock of walking, running, and other activity. Sometimes a rupture or herniation of a disk may occur ( see herniated disk).

Each vertebra consists of a front positioned body, also called the centrum, surmounted by a Y-shaped neural arch. The arch extends a spinous process (projection) downward and backward that may be felt as a series of bumps down the back, and two transverse processes, one to either side, which provide attachment for muscles and ligaments. Together the centrum and neural arch surround an opening, the vertebral foramen, through which the spinal cord passes. The centrums are separated by cartilaginous intervertebral disks, which help cushion shock in locomotion.

A semicircular arch of bone protrudes from the back of each vertebral body, surrounding the spinal cord. Directly in its midline a bony projection, the spinous process, grows backward from the arch. The spinous process can be felt on the back as a hard knob. Three pairs of outgrowths project from the arch. One of these protrudes horizontally on each side and in the thorax connects with the ribs. The remaining two form joints with the vertebrae above and below. The joints permit the spine to bend flexibly. The vertebrae are held firmly in place by a series of strong ligaments. (see figure to left).

The spine is designed to bend and turn. Along with the intervertebral discs, facet joints enable the spine to bend and twist. Each vertebra has two sets of facet joints. One set of facet joints is located at the top and a corresponding set is at the bottom.

Working like a hinge, the articulating surfaces of each facet joint are coated with smooth cartilage allowing friction free movement. Although the facet joint bones fit snugly together, there is a lubrication system. The lubricating 'oil' is called synovial fluid and resembles uncooked egg whites. This fluid also nourishes the cartilage tissues.

To view a detailed listing of the bones of the spine, click here.

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