Spinalnerv

Spinal nerve, in German often referred to as spinalnerv, is a mixed peripheral nerve formed by the union of the dorsal (posterior) and ventral (anterior) roots of a single spinal segment. In humans there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. The dorsal root carries sensory fibers and contains the dorsal root ganglion, which houses the cell bodies of sensory neurons. The ventral root contains motor fibers that innervate skeletal muscles. The dorsal and ventral roots merge to form a mixed spinal nerve that exits the spinal canal through the intervertebral foramen.

After exiting, each spinal nerve divides into a dorsal ramus, which supplies the back muscles and skin, and a ventral ramus, which supplies the anterior trunk and the limbs. In the thoracic region the ventral rami generally form intercostal nerves; in other regions they contribute to larger nerve networks called the cervical, brachial, lumbar, and sacral plexuses.

Spinal nerves convey somatic sensory and motor information, and also carry autonomic fibers that regulate targets such as blood vessels and organs via downstream pathways. Dermatomes describe the skin regions served by each spinal nerve, while myotomes describe the muscle groups activated by each spinal nerve.

Clinical relevance: injury or compression of a spinal nerve at a given level can cause radicular pain, numbness, weakness, or reflex changes in the corresponding dermatome and myotome. Common causes include herniated discs, degenerative changes, and traumatic injury.