B fiber

n.

Any of the myelinated nerve fibers in autonomic nerves, having a diameter of 2 microns or less, conducting nerve impulses at a rate of 3 to 15 meters per second.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.