1. nerve fibers, unmyelinated A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the unmyelinated nerve fibers are small. The axons to SCHWANN CELLS ratio is greater in the unmyelinated nerve fibers than that in the myelinated fiber (NERVE FIBERS, MYELINATED) which is 1:1. Usually several axons are surrounded by a single Schwann cell in the unmyelinated nerve fibers. Therefore, each unmyelinated fiber is not completely covered by the MYELIN SHEATH formed by the Schwann cell. Unmyelinated nerve fibers conduct impulses at low velocities. They represent the majority of peripheral sensory and autonomic fibers. They are also found in the spinal cord and brain.
Definitions of nerve fibers, unmyelinated
