sympathetic nervous system That part of the autonomic nervous system which generally acts to stimulate the body to cope with stress, such as increasing the rate of heart beat. Nerves of the sympathetic nervous system tend to form ganglia (ganglion) beside the vertebrae, preganglionic fibres leading from the spinal cord to the ganglia. The nerve endings are adrenergic in postganglion synapses and cholinergic in preganglion synapses. The sympathetic nervous system acts antagonistically to the parasympathetic nervous system.

sympathetic nervous system Part of the autonomic nervous system. Its nerve endings release noradrenaline or adrenaline as a neurotransmitter and its actions tend to antagonize those of the parasympathetic nervous system, thus achieving a balance in the organs they serve. For example, the sympathetic nervous system decreases salivary gland secretion, increases heart rate, and constricts blood vessels, while the parasympathetic nervous system has opposite effects.

sympathetic nervous system (sim-pă-thet-ik) n. one of the two divisions of the autonomic nervous system, having fibres that leave the central nervous system in the thoracic and lumbar regions and are distributed to the blood vessels, sweat glands, salivary glands, heart, lungs, intestines, and other abdominal organs. It is responsible for increasing the heart rate and dilating the pupil, among other effects.