Gray ramus communicans

Each spinal nerve receives a branch called a gray ramus communicans (pl.: rami communicantes) from the adjacent paravertebral ganglion of the sympathetic trunk. The gray rami communicantes contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons. This is in contrast to the white rami communicantes, in which heavily myelinated neurons give the rami their white appearance.

Preganglionic sympathetic fibers from the intermediolateral nucleus in the lateral grey column of the spinal cord are carried in the white ramus communicans to the paravertebral ganglia of the sympathetic trunk. Once the preganglionic nerve has traversed a white ramus communicans, it can do one of three things.

Ganglionic influence can be specifically targeted to end organs as well as becoming part of a summating systemic response. If the response is the whole body response, as in sympathetic fight or flight, the signals are distributed to other spinal nerves by way of gray rami communicantes which serve as conduits between the spinal nerves.

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

Wilson-Pauwels, Linda; Stewart, Patricia A.; Akesson, Elizabeth J. (January 1997). Autonomic Nerves. Canada: B. C. Decker, Inc. pp. 71–104. ISBN 978-1-55009-030-7.