Sympathetic and Parasympathetic Innervation to the Pelvis

Sympathetic innervation originates from lumbar roots L1 to L3. These fibers pass through the sympathetic ganglion and leave as lumbar sympathetic nerves that join the preaortic plexus. This extends caudally as the mesenteric plexus and then the superior hypogastric plexus. This plexus is formed both by the lumbar sympathetic nerves through the plexus and separately by lumbar splanchnic nerves (from the sympathetic chains). The plexus then divides into the two hypogastric nerves descending along the iliacs until joined by the parasympathetic nervi eri-gentes to form the pelvic or inferior hypogastric plexus.

Parasympathetic nerve fibers arise from the sacral nerve roots and emerge as pelvic splanchnic nerve or nervi eri-gentes, which join the sympathetic nerve to form a pair of inferior hypogastric (or pelvic) plexuses on each of the pelvic side walls. Fibers from this pelvic plexus (sympathetic and parasympathetic) then branch out and innervate the bladder, ureters, corpora cavernosa, and rectum. Somatic fibers also pass through the pelvic plexus to innervate the levators and ureteral striated muscles. These pelvic plexuses run anterolateral to the rectum necessitating close rectal dissection to avoid nerve injury.

The ischiorectal space is lateral to the perianal space. Its apex is formed by the joining of the levator and obturator muscles while the inferior boundary is the skin of the perineum. Anteriorly, it is bound by the transverse perineal muscles and posteriorly by the gluteal skin. This space contains the pudendal vessels and pudendal nerve in Alcock's canal. Alcock's canal, or the pudendal canal, is on the medial side of the obturator internus in the ischiorectal fossa.

The intersphincteric space is between the anal sphincters and communicates with the perianal space. Most of the anal glands are in the intersphincteric space.

The superficial postanal space connects the perianal spaces with each other below the level of the anococcygeal ligament. The deep postanal space, the right and left ischioanal/rectal spaces communicate with this space posteriorly deep to the anococcygeal ligament. Infection in this space leads to a horseshoe abscess.

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