Neural Control of the Lower Urinary Tract

The urinary bladder and its outlet, the urethra, serve 2 main functions: the storage of urine without leakage, and the periodic release of urine. These 2 functions are dependent on central as well as peripheral autonomic and somatic neural pathways.l-b Since the lower urinary tract switches, in an all-or-none manner, between storage and elimination of urine, many of the neural circuits controlling voiding exhibit phasic patterns of activity rather than the tonic patterns occurring in autonomic pathways to other viscera. Micturition is a special visceral mechanism because it is dependent on voluntary control, which requires the participation of higher centers in the brain, whereas many other visceral functions are regulated involuntarily. Because of these complex neural regulations, the central nervous system control of the lower urinary tract is susceptible to a variety of neurologic disorders. This paper reviews studies in animals and humans that have led to our current concepts of the neural mechanisms underlying urinary continence and micturition. In addition, the final section of the paper focuses on recent evidence indicating that plasticity in bladder afferent pathways is involved in the reorganization of the micturition reflex pathways in various pathologic conditions.