Innervation of the Bladder, Urethra and Pelvic Floor

Abstract

The innervation of the bladder and urethra is complex. There are components from the autonomic and from the somatic nervous systems. The pelvic floor, on the other hand, is innervated only by somatic efferent and afferent nerve fibres. The normal functioning of the urethral sphincter depends on co-ordinated action of the sphincter mechanism, consisting of a smooth, non-striated internal urinary sphincter and striated voluntary periurethral sphincter muscles, with appropriate relaxation and contraction of the detrusor musculature of the bladder wall. Thus, the autonomic and somatic nervous systems must be co-ordinated for appropriate function. The synthesis of activity necessary to produce this effect is a function of the central nervous system, both at spinal and brainstem levels. The act of micturition is under voluntary control, from cortically derived relaxation of the striated periurethral sphincter musculature at the commencement of the act of micturition. The periurethral striated sphincter musculature is under continuous tonic activation, thus resembling the external anal sphincter muscle and the puborectalis muscle. The abductor muscle of the larynx, the cricopharyngeus muscle, the stapedius, and the striated sphincter muscle of the diaphragm at the cardia are similarly under tonic continuous low-level activation. In order to function effectively, the bladder detrusor, and the sphincter musculature and its central motor connections require afferent input and this is achieved through both the autonomic and somatic nervous systems.