parasympathetic nervous system

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The part of the autonomic nervous system originating in the brain stem and the lower part of the spinal cord that, in general, inhibits or opposes the physiological effects of the sympathetic nervous system, as in tending to stimulate digestive secretions, slow the heart, constrict the pupils, and dilate blood vessels.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun neuroanatomy One of the divisions of the autonomic nervous system, based between the brain and the spinal cord, that slows the heart and relaxes muscles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun originates in the brain stem and lower part of the spinal cord; opposes physiological effects of the sympathetic nervous system: stimulates digestive secretions; slows the heart; constricts the pupils; dilates blood vessels