Axonal Conduction and Myelin

The association of myelin with the axon is perhaps the most intimate and well-studied functional relationship between a glial element and a neuron. Myelin is formed as membranous wraps around an axon in the peripheral nervous system by Schwann cells, which make a single segment of myelin, and in the central nervous system by oligodendrocytes that make multiple myelin segments. The membranous wraps formed by myelin confers a high resistance and low capacitance to a considerable length of a myelinated axon (internodal region) that greatly increases the conduction velocity and security of impulse conduction. In addition to myelinated axons there are nonmyelinated axons, which do not have myelin, are typically smaller in diameter and conduct at much reduced velocities.