Lecture 51: Sacral Plexus and Autonomic and Somatic Control of Urination and Defecation

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: Essay Questions : Individuals who experience uterine pain due to endometriosis can elect to have the superior hypogastric plexus surgically interrupted or cut to eliminate pain signals. Review autonomic innervation to pelvic viscera. Include three pathways for sympathetic innervation and one pathway for parasympathetic innervation. Differentiate between sacral and pelvic splanchnic nerves. : A 45 year old man suffers from atonic bladder following a motor vehicle accident. Describe the approximate location of the injury and the presentation of atonic bladder. Explain the process of micturition in your answer, including relevant nerves and anatomical pathways. : True False Questions : Neurogenic (autonomous) bladder results from injury at the S2-S4 spinal cord, causing disruption of the reflexes mediating urination. : Parasympathetic innervation causes dilation of the helicine arteries, which, in turn, causes an erection. : Sympathetic innervation to the internal urethral sphincter causes constriction during filling of the bladder and facilitates emission by constricting during ejaculation to prevent retrograde flow of semen. : The external anal sphincter is somatically innervated and is, thus, under voluntary control. : The Valsalva maneuver is a voluntary action to contract the abdominal musculature and increase intraabdominal pressure to facilitate the passing of feces. : The hypogastric nerves are not noted for conveying parasympathetic fibers from the aortic plexus, but the left hypogastric nerve conveys preganglionic parasympathetic fibers from the inferior hypogastric plexus. : Preganglionic parasympathetic cell bodies effecting the hindgut are located in the intermediolateral cell column of S2-4, whereas postganglionic cell bodies are located within the wall of the hindgut. : Preganglionic sympathetic cell bodies effecting the hindgut are located in the intermediolateral cell column of L1-L2, whereas postganglionic cell bodies are located within inferior mesenteric ganglia. : Pelvic splanchnic nerves convey preganglionic fibers from the ventral rami of S2-4 to the inferior hypogastric plexuses, whereas, the inferior hypogastric plexus, in turn, conveys preganglionic fibers to autonomic plexuses located of the surfaces of the the pelvic viscera. : Peritonealized regions of the pelvic viscera send nociceptive information along sympathetic pathways to upper lumbar and lower thoracic cord levels, whereas retroperitoneal regions send nociceptive information along parasympathetic pathways to S2-4 cord levels. : Retroperitoneal regions of the pelvic viscera are inferior to the pelvic pain line and, thus, send both nociceptive and homeostatic information along parasympathetic pathways to the S2-4 cord levels. : Transection of the left hypogastric nerve as a treatment for pelvic pain may risk the parasympathetic innervation to much of the hindgut. : Referred pain secondary to perturbation of retroperitoneal pelvic viscera may manifest along the posterior thigh, leg, and foot; reflecting the distribution of the S2 dermatome. : The "cerebral release mechanism" refers to a trigger point where cognitive factors relinquish inhibitory control of cord level reflexes. : A "bashful bladder" may be thought of as an instance of an overly inhibitory cerebral release mechanism; a helicopter cognitive influence over cord level reflexes. : The cognitive release of control over cord reflexes is triggered by somatic afferent information (GSA). : The micturition reflex is triggered by a build up of stretch information (GVA) from the bladder wall reflecting the extent that urine has accumulated in the bladder. : During micturition, the detrusor muscle, driven by parasympathetic influence, contracts and the internal urethral sphincter, driven by parasympathetic influence, relaxes. : Once the micturition reflex is triggered, urinary continence depends on somatic nerves and musculature. : Urine flow in the membranous and spongy urethra is sensed by somatic (GSA) nerves conveyed by the pudendal nerve, and this information provides a positive feedback loop that further drives the parasympathetic mediated contraction of the detrusor muscle, and further decreases somatic tone to the pelvic floor (lowers further) and to the external urethral sphincter (opens widely). : Somatic feedback during urine flow overcomes inhibition of cord level reflexes caused by cognitive factors - the cerebral release mechanism. : An atonic bladder results when sensory information regarding stretch from the bladder (GVA) is not available to act on preganglionic parasympathetic cell bodies to drive contraction of the detrusor muscle. : The atonic bladder may fill to the point of bursting and, thus, requires sectioning of parasympathetic preganglionic fibers to convert the atonic bladder to a neurogenic (autonomous) bladder. : Extreme filling of the atonic bladder is due to the intact parasympathetic preganglionic synapse never signaling the detrusor muscle to contract (waiting for Godot). : Somatic feedback regarding flow inferior to the dentate line by inferior rectal branches of the pudendal nerve, similar to micturition, evokes a positive feedback loop to further lower the pelvic floor (straighten the rectum), relax the puborectalis muscle (straighten and open the anal canal), further relax the external anal sphincter, intensify the strength of peristalsis of the hindgut, and overcome cognitive inhibition of cord reflexes.

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