Spinal Nerve Cross-Section

Thirty-one pairs of spinal nerves originate from the spinal cord. They are all mixed nerves, and they provide a two-way communication system between the spinal cord and parts of the arms, legs, neck, and trunk of the body. These nerves are actually single cells that have the function of carrying information from one area of the body to another area. Most of these cells are grouped together like the strands of a rope. Nerve cells have the same basic structure as all the other body cells, with...

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Full Spinal Nerve Cross-Section Description

[Continued from above] . . . a surrounding membrane containing the nucleus and cytoplasm, but they have a very special, elongated shape.

Although spinal nerves do not have individual names, they are grouped according to the level from which they stem, and each nerve is numbered in sequence. Hence, there are eight pairs of cervical nerves (numbered C1 - C8), twelve pairs of thoracic nerves (T1 - T12), five pairs of lumbar nerves (L1 - L5), five pairs of sacral nerves (S1 - S5), and one pair of coccygeal nerves.

Each spinal nerve emerges from the cord by two short branches or roots, which are within the vertebral column. A ventral root and a dorsal root unite to form a spinal nerve that exits the vertebral canal through an opening called the intervertebral foramen. The nerves coming from the upper part of the spinal cord pass outward nearly horizontally, while those from the lower regions descend at sharp angles. This is a consequence of a child's growth patterns. In early life, the spinal cord extends the entire length of the vertebral column, but with age, the column grows faster than the cord. As a result, the adult spinal cord ends at the level between the first and second lumbar vertebrae, so the lumbar, sacral, and coccygeal nerves descend to their exits beyond the end of the cord.