Abstract
This communication reviews new concepts of micturition and continence mechanisms which we have recently advanced. The role of the pelvic floor musculature in micturition and continence is outlined. The vesical neck is related to two muscles of ‘micturition’: the longitudinal and levator ani muscles, and another two of ‘continence’: the internal sphincter and the puborectalis. The mechanism of urinary continence is described. The voluntary sphincter complex (VSC), (puborectalis and external urethral sphincter) induces continence by voluntary inhibition action (VIA) and mechanical compression action. The involuntary action of the VSC after internal sphincter excision is emphasized. Although the micturition mechanism is mediated and coordinated by multiple reflex actions, it is yet under voluntary control. The micturition and vesicolevator reflexes function to open the vesical neck, while the vesicopuborectalis and levator-urethral reflexes as well as the VIA keep the vesical neck closed until the decision to urinate is made. Straining at micturition evokes the straining-levator reflex which causes levator contraction and vesical neck opening. The role of the dilatation and closing reflexes in urinary continence and stress incontinence is discussed.
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