Somato-motor components of the pelvic and pudendal nerves of the female rat.

The efferent innervation of the pelvic and pudendal nerves was characterized in this study by identifying the muscles activated by electrical stimulation of the nerves distal to the point at which they bifurcate from the L6-S1 trunk. Pelvic nerve electrical stimulation produced EMG-monitored contraction of the ipsilateral ilio- and pubococcygeus muscles, which was abolished by cutting one ('muscular') branch of the bifurcated nerve. (This 'muscular' branch receives proprioceptive input activated by tail displacement, whereas the other, 'viscero-cutaneous' branch receives sensory innervation from the midline perineal region.) Pudendal nerve electrical stimulation produced contraction of the coccygeus, external anal sphincter, and ischiocavernosus muscles. Movements of the orifice and wall of the vagina were directly visualized during electrical stimulation of the two nerves. Intravaginal pressure measured by balloon was increased by pelvic nerve stimulation and decreased by pudendal nerve stimulation. Reflexive contraction of the ilio- en pubococcygeus muscles was produced by mechanostimulation of the perineum, clitoral sheath and distal vagina. This response was abolished by gentle cervical mechanostimulation. One implication of this finding is that passage of the fetuses through the cervix during parturition may relax the ilio- and pubococcygeus muscles, thereby facilitating delivery.