A Horses Tail Of Nerve Roots - The Anatomy Of Your Back: Back Pain

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A horse's tail of nerve roots

Although the spinal cord, or central nerve trunk, extends from the brain only to the upper part of the lumbar spine, right and left spinal nerve roots continue downward to the end of the spine.

The nerve roots in the lumbar spinal canal form a bundle of strands resembling a horse's tail — hence the name cauda equina, which is Latin for horse's tail (see Figure 3B). These nerve roots contain the nerve fibers that control your leg muscles and play important roles in bladder, intestinal, and genital functions. Similarly, your sensory nerve fibers, which provide feeling from your toes up to your hips, travel through these same nerve roots on their way to your spinal cord and from there to your brain.

Nerve-root compression

Although the spine provides a protective canal for the nerve roots and spinal cord, it may also endanger these very structures. For a variety of reasons, the conduit can become too narrow, pressing on and pinching the nerve roots and their related nerve tissues. Pinched or irritated nerve roots within or near the lumbar vertebrae may cause low back or leg pain.

Various types of problems can cause this kind of painful nerve-root compression (see Figure 4). For example, a disk can bulge in such a way that it pinches a nerve or protrudes into the spinal canal. Or a defect in the outer covering of the disk can result in a displacement of part of the disk, which can cause severe nerve-root pressure. Degenerative arthritis of the small joints coupled with the formation of small bone spurs (called osteophytes) around them can also compress one or more nerve roots. This problem is especially likely to occur in the two narrow channels, one on each side, between adjacent vertebrae, known as the intervertebral foramina.

Figure 4: Compression of nerve roots Nerve roots can be painfully compressed in several ways. Among the various causes of compression are arthritis of the facet joints (A), an osteophyte or bone spur (B), and a herniated — or bulging — intervertebral disk (C).

It's also possible for one or more nerve roots to be squeezed by one or more bulging disks or bone spurs within the canal of the lumbar spine itself. This causes the spinal canal to narrow, compressing nerves and causing a problem known as spinal stenosis. The stenosis may occur between two vertebrae or involve almost the entire circumference of the spinal canal at one or more levels.

Last updated:	January 23, 2007