Chapter 8 - Nerve Fiber Types

Abstract

Within a peripheral nerve there are both myelinated and nonmyelinated nerve fibers. Nerves vary in their relative composition of myelinated and nonmyelinated fibers from one anatomical site to another. Both types of fibers are supported by Schwann cells. The axons in the peripheral nerves also vary in size and conductance velocity; from nonmyelinated axons less than 1μm in diameter with conducting action potential less than 1m/s to heavily myelinated 20-μm axons with conducting action potential 100m/s. Myelinization and diameter of axons affect the conduction velocity of nerve fibers. Moreover, a number of other functional characteristics are used to categorize nerve fibers into distinct groups. These include the direction of transmission of signals in relationship to the central nervous system and divides nerve fibers into afferent (projecting to the central nervous system) and efferent (projecting to the periphery). Moreover, fibers are classified into somatic and visceral. Based on these parameters, several anatomical and physiological classifications of nerve fibers were introduced into the literature.