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Normal micturition occurs when bladder contraction is coordinated with urethral sphincter relaxation.

Normal micturition occurs when bladder contraction is coordinated with urethral sphincter relaxation.
Normal micturition occurs when bladder contraction is coordinated with urethral sphincter relaxation.

The CNS inhibits voiding until the appropriate time and coordinates and facilitates input from the lower urinary tract to start and complete voiding. The sympathetic system contracts the smooth muscle sphincter. The parasympathetic nervous system contracts the bladder detrusor muscle through cholinergic fibers. The somatic nervous system contracts the striated muscle sphincter through cholinergic fibers from the pudendal nerve. (Adapted from DuBeau CE, Resnick NM with the Massachusetts Department of Health EDUCATE project collaborators: Urinary Incontinence in the Older Adult: An Annotated Speaker/Teacher Kit , 1993; used with permission of the authors.)