Anatomy of spinal nerves exiting through the intervertebral foramina

The spinal cord is an extension of the brainstem (the lowest part of the brain), extending from the base of the skull down to the low back. Along its length, it gives off 31 pairs of spinal nerves, which branch to form the peripheral nerves of the neck, trunk, and extremities. The origins of the spinal nerves as they emerge from the spinal cord are called nerve roots.

This image shows a dissection of the cervical region, showing a posterior view of cervical spinal nerves exiting the intervertebral foramina on the right side.

The spinal nerves exit from the vertebral column through openings between adjacent vertebrae. These openings, called intervertebral foramina, are located just in front of the facet joints. The spinal nerves are named and numbered according to the vertebral levels at which they exit. There are eight paired cervical nerves (C1-C8), twelve thoracic (T1-T12), five lumbar (L1-L5), five sacral (S1-S5), and one coccygeal (Co1).

Note :

-There are eight pairs of cervical nerves, although there are only seven cervical vertebrae. The C1 nerves exit above the C1 vertebra (between C1 and the base of the skull).
-Although the spinal nerves correspond to their respective vertebral levels, the spinal cord itself is shorter than the vertebral column, extending only as far as the L1 vertebra. Below that level, the spinal canal contains only the roots of the lumbar, sacral, and coccygeal nerves, as they descend to exit at the appropriate levels. This bundle of descending nerve roots is called the cauda equina (Latin for "horse's tail").

The on the right views a portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots.

Nerve Roots:—

Each nerve is attached to the medulla spinalis by two roots, an anterior = ventral, and a posterior = dorsal, the latter being characterized by the presence of a ganglion, the spinal ganglion.