1. the narrow line along the course of a nerve (or nerve root) where the Schwann cells and connective tissue that support its axons are replaced by glia cells. The zone marks the true boundary between the central and the peripheral nervous system. Usually located at or near the surface of the spinal cord or brainstem, it can extend (in the eighth cranial nerve) several millimeters out along the nerve.
Stedman’s Medical Dictionary © Wolters Kluwer Health. All rights reserved.