Functional anatomy and neural regulation of the lower urinary tract in female dogs: a review.

A review of the literature of the functional anatomy and neural regulation of the lower urinary tract is presented. The two main functions of the lower urinary tract are the storage and the periodic elimination of urine. The smooth muscle of the bladder exhibits intermittent contractions as the bladder adapts its capacity to increasing volumes and it exhibits sustained contractions associated with relaxation of the external sphincter to effect micturition. During storage, tension receptors in the bladder wall initiate external sphincter contraction (somatic), internal sphincter contraction (sympathetic), detrusor inhibition, and parasympathetic ganglion inhibition (sympathetic). The storage phase can be switched to the micturition phase either voluntarily or involuntarily. Neuroanatomical and electrophysiological studies reveal that medial and lateral cell groups in the dorsolateral pons may be regarded as micturition and storage control centres, respectively.