the speed at which nerve impulses travel along the axon of a neuron. Measurements by various techniques show that axons vary considerably in velocity of conduction, from 80 to 120 m/s for large, myelinated A fibers to 0.5 to 2 m/s for small, unmyelinated C fibers. Conduction velocity was first measured by Hermann von Helmholtz. See also peripheral nerve fiber classification.