Axon

An axon, or "nerve fiber," is a long slender projection of a nerve cell or neuron, which conducts electrical impulses away from the neuron's cell body or soma. Although they may be more than a yard in length, the diameter is microscopic. They may divide into branches called axon collateralwhich extends out to allow divergence, signaling by a single neuron to many, to occur. Axons are in effect the primary transmission lines of the nervous system, and as bundles they help make up nerves.

The axons of many neurons are sheathed in myelin formed by Schwann cells. The wrapping around of the Schwann cells is what is termed mylenation. Mylenation occurs to those with diameter of 2nm or more but those smaller are unmyelinated. The gaps between each successive Schwann cells are called nodes of Ranvier.

The longest axons in the human body are those of the sciatic nerve that run from the base of the spine to the big toe of each foot. These single-cell fibers may extend a meter or even longer.

Compare dendrite.