Autonomic Nerves and Ganglia in Pelvis

Sympathetic Fibers. The lumbar and sacral parts of the sympathetic trunks are directly continuous at the level of the pelvic brim. The sacral trunks lie in the pelvic fascia behind the parietal peritoneum and rectum, and on the anterior surface of the sacrum, just medial to its anterior foramina and the nerves and vessels passing through them. Below, they converge and unite in a single tiny “ganglion impar” anterior to the coccyx. In general, four, or sometimes, three sacral trunk ganglia exist on each side. No white rami communicantes are present in this region, but each ganglion supplies one or more gray rami communicantes containing postganglionic sympathetic fibers to the adjoining sacral and coccygeal spinal nerves; these fibers are conveyed in branches of the sacral and coccygeal plexuses to vessels, sweat glands, arrectores pilorum muscles, striated muscles, bones, and joints.

The pelvic sympathetic trunk ganglia also supply slender rami, the sacral splanchnic nerves, which pass to the inferior hypogastric plexuses. The majority of sympathetic fibers, however, reach these plexuses through the right and left hypogastric nerves, formed just below the level of the lumbosacral junction by the splitting of the median superior hypogastric plexus (often misleadingly referred to as the “presacral nerve”—a single nerve is very rare). Similarly, the right and left hypogastric nerves are more often elongated plexuses consisting of several nerves interconnected by oblique strands, which incline downward on each side, behind the peritoneum and lateral to the sigmoid colon and rectosigmoid junction, to end in the upper parts of the homolateral inferior hypogastric plexus.

The inferior hypogastric plexuses are situated on each side of the rectum, lower part of the bladder, prostate, and seminal vesicles. In females, the cervix of the uterus and vaginal fornices replace the prostate gland and seminal vesicles as medial relations. The plexuses supply branches to the pelvic viscera and genitalia and often form subsidiary plexuses (such as the rectal, prostatic, and vesical). The branches contain visceral, glandular, vascular, and afferent fibers, often combined in the nerve fascicles supplying the various structures concerned (see Plates 7-21 to 7-24). The sympathetic efferent fibers in these branches, like those in the gray rami communicantes connecting the ganglia of the pelvic sympathetic trunks to the sacral and coccygeal spinal nerves, are almost entirely postganglionic because most or all of the sympathetic preganglionic fibers involved in the supply of pelvic, perineal, gluteal, and lower limb structures relay in lumbar and sacral trunk ganglia; a minority may form synapses in ganglia within the inferior hypogastric plexuses.

The parasympathetic fibers in the pelvic splanchnic nerves, which arise from the sacral nerves and end in the inferior hypogastric plexuses, are preganglionic. Some relay in ganglia within the plexuses, but many more form synapses in ganglia located near or within the walls of the viscera and vessels innervated.

Other branches from the inferior hypogastric plexuses ascend to assist in the innervation of the distal colon and the renal pelvises.

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