Spinal nerves are mixed nerves that originate from the spinal cord.
A typical nerve begins as dorsal roots having sensory fibers and ventral roots containing motor fibers.
These roots merge, forming a spinal nerve that exits the vertebral column through the intervertebral foramen.
The spinal nerve further divides into a smaller posterior ramus and a large anterior ramus.
The posterior ramus serves the muscles and skin of the posterior side of the torso. In contrast, the anterior ramus serves the limbs, skin, and muscles of the anterior and lateral sides.
Tiny meningeal branches reenter the vertebral column to supply the vertebrae, associated ligaments, and spinal cord-associated blood vessels.
There are 31 pairs of spinal nerves, numbered according to the vertebrae they exit. These include eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal nerve.
Except for T2 to T12, the axons of the anterior rami of the adjacent spinal nerves form networks or plexuses before innervating the body parts.
The major nerve plexuses include the cervical, brachial, lumbar, sacral, and coccygeal plexuses.
Spinal nerves are pivotal conduits in the nervous system, bridging the central nervous system (CNS) with the peripheral nervous system (PNS). These nerves enable a complex communication network between the brain, spinal cord, and the rest of the body, facilitating sensory input, motor output, and autonomic functions.
There are 31 bilateral pairs of spinal nerves, each emerging from the spinal cord through the intervertebral foramina—openings between adjacent vertebrae. These nerves are symmetrically organized and are categorized based on the region of the spine from which they emerge — 8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (Co1).
Structure of Spinal Nerve
Each spinal nerve is formed by the union of two distinct roots — the dorsal (posterior) root and the ventral (anterior) root.
These two roots combine to form a mixed spinal nerve carrying both sensory and motor fibers. Shortly after emerging from the spinal column, each spinal nerve splits into two primary branches — the dorsal ramus and the ventral ramus.
Additionally, each spinal nerve has a small meningeal branch that reenters the vertebral column to innervate the vertebrae, ligaments, blood vessels, and meninges of the spinal cord. Spinal nerves also feature communicating rami that connect with the sympathetic trunk of the autonomic nervous system (ANS). These rami consist of: