Pertaining to that part of the nervous system consisting of nerves and ganglia that arise from the cranial and sacral regions and generally function in regulatory response to the sympathetic system; in the eye, causes contraction of the pupil of the eye.
Part of the nervous system that, together with the sympathetic nervous system, forms the autonomic nervous system (ANS). The ANS controls the functioning of involuntary structures, including the heart, glands, and smooth muscle. The parasympathetic nervous system regulates nerve transmissions to certain effector organs under normal conditions, as opposed to times of stress. It serves to "steady" involuntary activities and conserve or restore energy. Parasympathetic responses may include slowing of the heart and breathing rates, contraction of the pupils, an increase in glandular activity, and an acceleration in the rate of peristalsis.