Parasympathetic Nervous System - Pelvic Splanchnic Control

Pelvic Splanchnic Control

The pelvic splanchnic nerves, S2-4, work in tandem to innervate the pelvic viscera. Unlike in the cranium, where one PSN was in charge of one particular tissue or region, for the most part the pelvic splanchnics each contribute fibers to pelvic viscera by first traveling to one or more plexuses before being dispersed to the target tissue. These plexuses are composed of mixed autonomic nerve fibers (PSN and SN) and include the vesical, prostatic, rectal, uterovaginal, and inferior hypogastric plexus. The preganglionic neurons in the neurons do not synapse in named ganglion as in the cranium but rather in the walls of the tissues or organs that they innervate. The fiber paths are variable and each individual's autonomic nervous system in the pelvis is unique. The visceral tissues in the pelvis that the PSN control include: urinary bladder, ureters, urinary sphincter, anal sphincter, uterus, prostate, glands, vagina and penis. Unconsciously, the PSN will cause peristaltic movements of the ureters helping to move urine from the kidneys into the bladder and move feces down the intestinal tract and upon necessity, the PSN will assist excreting urine from the bladder or defecation. Stimulation of the PSN will cause the detrusor muscle (urinary bladder wall) to contract and simultaneously relax the internal sphincter urethrae muscle to relax allowing void of urine. Also, PSN stimulation to the internal anal sphincter will relax this muscle and allow defecation. There are other skeletal muscles involved with these processes but the PSN play a huge role in continence.

Another role that the PSN play in the pelvis is in sexual activity. In males, the cavernous nerves from the prostatic plexus stimulate smooth muscle in the fibrous trabeculae of the coiled helicene arteries to relax and allow blood to fill the corpora cavernosum and the corpus spongiosum of the penis, making it rigid to prepare for sexual activity. Upon emission of ejaculate, the sympathetics participate and cause peristalsis of the ductus deferens and closure of the internal urethral sphincter to prevent semen from entering the bladder. At the same time, parasympathetics cause peristalsis of the urethral muscle, and the pudendal nerve causes contraction of the bulbospongiosus (skeletal muscle is not via PSN), to forcibly emit the semen. During remission the penis becomes flaccid again. In the female, there is erectile tissue analogous to the male yet less substantial that plays a large role in sexual stimulation. The PSN cause release of secretions in the female that decrease friction. Also in the female, the parasympathetics innervate the fallopian tubes, which helps peristaltic contractions and movement of the oocyte to the uterus for implantation. The secretions from the female genital tract aids in semen migration. The PSN (and SN to a lesser extent) play a huge role in reproduction.