The Maximization of Nerve Conduction Velocity

Histological and electrical examination of high-speed (myelinated) nerve fibers reveals a coaxial RC cable whose inner conductor has from 40 to 80 percent of the diameter of the outer conductor. If various reasonable engineering approximations are made, it turns out that the latter geometry corresponds to maximum conduction velocity. The model suggests that this was the basis for selection by evolutionary processes. It is shown that the measured velocity of 6 × 106 diameters per second is consistent with a node-to-node transit time of 14.2 μs, unregenerated signal loss of 4.6 dB, and spacing of 85 diameters.