Part of the autonomic nervous system. Its nerve endings release acetylcholine as a neurotransmitter and its actions tend to antagonize those of the sympathetic nervous system. For example, the parasympathetic nervous system increases salivary gland secretion, decreases heart rate, and promotes digestion (by increasing peristalsis)—‘rest and digest’—while the sympathetic nervous system has opposite effects. However, in relation to reproductive function the PNS promotes erection of genitalia, thus complementing the action of the sympathetic system, which promotes ejaculation and vaginal contractions. Anatomically the preganglionic neurons of the PNS originate from the cranial nerves and from the lowest (sacral) region of the spinal cord, compared with the thoracic and lumbar regions of the spinal cord for the sympathetic division. Also, its ganglia lie close to the target organs, rather than alongside the spinal cord.