Autonomic Innervation of the Rectum: The rectal plexus is an offshoot of the posterior portion of the inferior hypogastric plexus. Nerves run from the inferior hypogastric plexus and penetrate the walls of the rectum providing enteric plexuses like those found in other parts of the intestines. Pelvic splanchnics (parasympathetics) innervate the internal anal sphincter that surrounds the upper two-thirds of the anal canal. During most times the internal anal sphincter is tonically contracted to prevent leakage of feces. Following distention of the rectal ampulla, the sphincter relaxes and then it is the job of the external anal sphincter, which is under voluntary control and supplied by the inferior rectal branches of the pudendal nerve, to prevent defecation.
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