Spinal nervesemerge from the segments of the spinal cord. They are numbered according to their specific segment of origin. Hence, the 31 pairs of spinal nerves are divided into 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs, and 1 coccygeal spinal nerve. All spinal nerves are mixed, containing both sensory and motor fibers.
Spinal nerves innervate the entire body, with the exception of the head. They do so by either directly synapsing with their target organs or by interlacing with each other and forming plexuses. There are four major plexuses that supply the body regions;
- Cervical plexus (C1-C4) – innervates the neck
- Brachial plexus (C5-T1) – innervates the upper limb
- Lumbar plexus (L1-L4) – innervates the lower abdominal wall, anterior hip and thigh
- Sacral plexus (L4-S4) – innervates the pelvis and the lower limb