14 - Nerve Roots

Abstract

This chapter outlines the development and adult anatomy of the nerve roots. The neuroepithelium of the embryonic cord undergoes mitotic activity in the inner ventricular zone. The developing dorsal horn receives central processes of neural crest-derived spinal ganglion cells. The ventral horn issues axons that form ventral nerve roots. The outer marginal zone contains the axons of developing nerve pathways. The caudal end of the cord develops separately from the caudal cell mass, which links up with the neural tube. The result is a progressive disparity between segmental levels of nerve root attachment to the cord and intervertebral levels of exit of spinal nerves. The mature cord and nerve roots are sheathed by the pia mater and suspended in the subarachnoid space, anchored to the dura by the denticulate ligament. As it emerges from the intervertebral foramen (occupied by the posterior root ganglion), each spinal nerve gives a recurrent branch supplying ligaments and dura mater. Segmental sensory distribution is shown by the regular dermatomal pattern of skin innervation by the posterior roots (via the mixed peripheral nerves). Segmental motor supply is expressed in the form of movements performed by specific muscle groups. Nerve root compression may be expressed segmentally by muscle pain, dermatomal paraesthesia, cutaneous sensory loss, motor weakness, or loss of a tendon reflex. A spinal anaesthesia is given by injecting local anaesthetic into the lumbar cistern, an epidural anaesthesia is given into the lumbar epidural space, and caudal anaesthesia is given through the sacral hiatus.