noun
or parasympathetic system
: the part of the autonomic nervous system that contains chiefly cholinergic fibers and tends to induce secretion, increase the tone and contractility of smooth muscle, and cause the dilatation of blood vessels and that consists of a cranial part made up of preganglionic fibers leaving and passing the midbrain by the oculomotor nerves and the hindbrain by the facial, glossopharyngeal, vagus, and accessory nerves and passing to the ciliary, sphenopalatine, submaxillary, and otic ganglia of the head or to ganglionated plexuses of the thorax and abdomen and post ganglionic fibers passing from these ganglia to end organs of the head and upper trunk and a sacral part made up of preganglionic fibers emerging and passing in the sacral nerves and passing to ganglionated plexuses of the lower trunk and postganglionic fibers passing from these chiefly to the viscera of the lower abdomen and the external genital organs — compare sympathetic nervous system