The spinal nerve is the nerve stem that exits the vertebral canal through an intervertebral hole and that divides inside the intervertebral hole into a hind root and a front root. The spinal nerves are symmetrically arranged on both sides of the midline. There are 31(sometimes 32-33) pairs of spinal nerves.
* 8(Note!) pair of carotid spinal nerves (cervical).
* 12 pairs of thoracic spinal nerves (thoracical).
* 5 pairs of lumbar spinal nerves (lumbar).
* 5 pairs of sacral spinal nerves (sacral).
* 1(-3) tail spinal nerves (coccygeal).
Once outside the vertebral column, the spinal nerve trunk divides into a posterior (dorsal) and an anterior (ventral) main branch.
The spinal nerves and its branches contain both motor and sensory nerve fibers.
Each spinal nerve receives, right next to the vertebral column, a so-called gray connecting branch that connects the spinal nerve to the sympathetic boundary cord. Through this grey branch of the connection, the spinal nerve is supplied with postganglionic sympathetic filaments from the border cord, which are then distributed to the skin and skeletal muscle with the help of the various branches of the spinal nerve.
The posterior spinal nerve branch (ramus dorsalis) is a rather thin branch that departs from the spinal nerve near the vertebral column. The posterior spinal nerve branches supply the skin and musculature of the neck and back.
The anterior spinal nerve branch (ramus ventralis) is the main branch of the spinal nerve. The anterior spinal nerve branches from
1) the spinal nerves C1 through C4 form the cervical plexus which gives rise to the skin and skeletal muscle nerves of the neck;
2) the spinal nerves C5 through T1 form the brachial plexus that gives rise to the skin and skeletal muscle nerves of the shoulder and arm;
3) the spinal nerves T2 through T12 form the rib nerves (nervi intercostales),
4) the spinal nerves L1 through S3 form the lumbo-sacral plexus that gives rise to the skin and skeletal muscle nerves of the hip and leg; and
5) the spinal nerves S4 to Co1(3) form the coccygeus plexus, which gives rise to the nerves of the external genitalia.