| Just distal to the dorsal root ganglia, the dorsal and ventral roots unite to form the 31 pairs of spinal nerves. Therefore, spinal nerves are mixed nerves, carrying both afferent fibers and efferent fibers. This is the closest mixed nerve to the spinal cord; the dorsal roots contain only afferent fibers and the ventral roots contain only efferent fibers. The spinal nerves are extremely short. They project laterally for only about 1-2mm before branching into dorsal and ventral primary rami as they exit the intervertebral foramina. The membranes covering the spinal cord become continuous with the layers surrounding the spinal nerves. The dura extends into the intervertebral foramina along the dorsal and ventral roots to form dural sleeves which eventually blend with the epineurium of the spinal nerves. The spinal nerves are a critical component of the nervous system, acting as the only path of communication between the peripheral nerves and the spinal cord. |
