The Spinal cord receives information from trunk and limbs and controls the movement of the trunk and limbs.
It has 31 paired Spinal nerves.
Formation of the spinal nerve
Two linear series (6 - 8) of nerve fascicles are attached to the dorsolateral and ventrolateral aspects of the cord.The fascicles coalesce to form dorsal and ventral nerve roots.
The roots pass to their corresponding intervertebral foramina, near which they join to form the spinal nerve proper.
Carry primary afferent neurons from the peripheral sensory receptors to the spinal cord and brain stem.
Their cell bodies are in the dorsal root ganglia.
Ventral root
Carry :
1.Efferent neurons (Lower motor neurons), their cell bodies are located in the spinal gray matter.
2.Preganglionic autonomic neurons
Rami
Spinal Nerves are mixed.They contain both afferent and efferent fibers.
Each spinal nerve is divided into dorsal and ventral rami.
Dorsal ramus: It is thin. supplies muscles and skin of the back.
Ventral ramus:Is larger, supplies muscles and skin of the front of the body and limbs.Connected to the sympathetic chain by the white and grey rami.
The spinal cord is segmented.
In the living, the approximate level of the segments is identified by the posterior spinous process of the vertebrae.
Cervical segments : One spine higher than their corresponding vertebrae. C7 segment is adjacent to C6 vertebra.
Thoracic segments : Two spines higher.
Lumbar segments : Three- four spines higher.
Exit of spinal nerves
1-7 spinal nerves : Exit above the upper seven cervical vertebrae.
C8 : Below 7th cervical vertebra.
T1 and the rest of the nerves: Below their corresponding vertebrae.
The Lumbar and Sacral nerves take an oblique course to reach the intervertebral foramina.
The resulting leash of nerve roots forms the Cauda Equina
