The urinary bladder is innervated by the pelvic and hypogastric nerves. The pelvic nerve is composed of efferent and afferent parasympathetic fibers. The efferent (motor) fibers innervate the detrusor muscle, which contracts to void urine. The afferent (sensory) fibers detect distention of the bladder wall as well as pain. The hypogastric nerve is composed of sympathetic fibers. Sympathetic stimulation has little influence on normal micturition but provides information on bladder distention and pain. Sensory receptors are located in the bladder mucosa, highly concentrated in the ureterovesical junction and bladder neck. When the mucosa is inflamed the hypogastric nerve transmits pain and urgency to urinate, even when the bladder is empty.

The urethra is innervated by the pudendal nerve, a mixed somatic nerve that contains motor fibers to the external urethral sphincter. Contraction of the urethral sphincter maintains urinary continence, but during micturition it relaxes due to inhibition of the pudendal nerve. Sensory receptors in the urethral mucosa sense the flow and temperature of urine as well as the distention of the urethra, providing the awareness of voiding. Inflammation of the urethral mucosa causes pain, a burning sensation, and spasms of the urethral sphincter.