The functional state of the lower urinary tract is monitored more or less continuously by afferent nerves, which provide a sensory input in the control of the bladder and the external urinary sphincter. The functional state of the former is regulated by the autonomic nerves to the bladder, principally the parasympathetic (pelvic) nerves, which cause the detrusor muscle to contract, and possibly also by the sympathetic (mainly hypogastric nerve) innervation, which may reduce the resting tone of the smooth muscle. Continence is normally maintained by the resistance of the urethral sphincters; the tone generated by the skeletal muscle external sphincter is under the control of the somatic [alpha]-motoneurones running in the pudendal nerve, and possibly some somatic efferents in the pelvic nerve of some species.