Anatomy, neurophysiology, and pharmacological control mechanisms of the bladder

The lower urinary tract has two main functions; the collection and low pressure storage of urine and periodical controlled elimination of urine at an appropriate time. In order to achieve continence during bladder filling and storage and produce efficient and effective bladder emptying, there is accurate coordination between opening and closing of the urethral sphincters and contraction of the detrusor smooth muscle. The process of micturition has two phases: the storage/filling phase and the voiding phase. The analogy for the transition between these two phases has been described as an on-off circuit, rather akin to flicking a light switch, between synchronous bladder contraction and urethral outlet relaxation, and vice versa. These phases are regulated by a complex, integration of somatic and autonomic efferent and afferent mechanisms that coordinate the activity of the bladder and urethra. This chapter provides an overview of our current understanding of these complex mechanisms.