The neural circuitry of the enteric plexuses permits coordinated activity in the isolated intestine, but normal function depends on intact autonomic control . Sympathetic postganglionic neurons generally use norepinephrine as their neurotransmitter. Sympathetic postganglionic neurons that supply sweat glands use acetylcholine. Parasympathetic postganglionic neurons use acetylcholine. The pupil is controlled reciprocally by the sympathetic and parasympathetic nervous systems.
Sympathetic activity causes mydriasis and parasympathetic activity causes meiosis.
The sympathetic pathway can be activated by excitement or pain. Parasympathetic pathways are involved in the pupillary light reflex and in accommodation. Emptying of the urinary bladder depends on parasympathetic outflow during the micturition reflex. Sympathetic constriction of the external sphincter of the urethra prevents voiding. The micturition reflex is triggered by stretch receptors and is controlled in normal adults by a micturition center in the pons.