The spinal nerves supply specific areas with motor and sensory function (Fig. 1.2).
There are 31 pairs of n e r v e s : eight cervical, 12 thoracic, five lumbar, five sacral and one coccygeal. While there are seven cervical vertebrae, eight cervical nerves (pairs) leave the spinal cord. The first cervical nerve pair
(C1) exits between the atlas and occiput.
Nerve pairs C2 through C7 are named to correspond to the vertebrae that sit beneath their exit points. The eighth pair (C8) exits between the seventh cervical and first thoracic vertebra. Starting from the first thoracic vertebra, nerve pairs are named to correspond to the vertebra located above their exit point.
Spinal nerves vary in diameter. The thickest ones are the nerves that lead to the arms and legs:
• the lower cervical nerves (C4-C8) and the upper thoracic nerve (Tl), which
lead to the upper extremity;
• the lower lumbar (L1-L5) and upper sacral nerves (S1-S2), which lead to the
lower extremity.
With the exception of Tl, which is thicker, all thoracic nerves are of the same caliber. The thinnest nerves are the coccygeal nerves.

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