Innervation of the striated muscle of the membranous urethra of the male dog

PURPOSE: To identify the functional innervation of the striated muscle layer of the post-prostatic urethra of male dogs. MATERIALS AND METHODS: Detailed anatomic dissection of the pelvic and pudendal nerves was carried out. The pressure and contractile responses to stimulation of these nerves were recorded in vivo and in vitro. RESULTS: Small branches of the pelvic nerve entered the membranous urethra but passed through the striated muscle to the inner smooth muscle layer. Stimulation of the nerve with 1 msec pulses at 10 Hz produced a slow contraction of the urethra which was unaffected by d-tubocurarine. Pudendal nerve branches entered the striated layer from the caudal end. Stimulation produced a rapid, visible contraction that was abolished by d-tubocurarine. Field stimulation of isolated strips of striated muscle resulted only in rapid, d-tubocurarine sensitive contractions. CONCLUSIONS: The striated muscle of the membranous urethra is innervated exclusively by the pudendal nerve.