accelerator fiber

n.
  1. Any of the postganglionic sympathetic nerve fibers that originate in the superior middle and inferior cervical ganglia of the sympathetic trunk and convey impulses to the heart that tend to increase the rapidity and force of the cardiac pulsations.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.