Innervation of Male Reproductive Organs

Sympathetic preganglionic fibers are the axons of intermediolateral column cells located in the lowest two or three thoracic and upper one or two lumbar segments of the spinal cord. They emerge in the anterior nerve roots of the corresponding spinal nerves and leave them in white rami communicantes passing to adjacent sympathetic trunk ganglia. They course via the thoracic and the upper lumbar splanchnic nerve, the celiac, intermesenteric (aortic) and superior hypogastric plexuses, and the hypogastric nerves to the inferior hypogastric (pelvic) plexuses. Many of these fibers relay in the lowest thoracic and upper lumbar sympathetic trunk ganglia or within the celiac plexus, but others do not relay until they reach ganglia in the inferior hypogastric plexuses. Consequently, the postganglionic fibers to the pelvic organs may be either long or relatively short. A minority of the sympathetic fibers for the pelvic viscera descend in the sympathetic trunks to emerge in the tiny sacral splanchnic nerves and thus join the inferior hypogastric plexuses.

Preganglionic parasympathetic fibers reach the inferior hypogastric plexuses in pelvic splanchnic nerves arising from the second, third, and fourth sacral spinal nerves. Nerve fibers from the inferior hypogastric plexuses supply the genital organs, and most of them relay in ganglia close to the prostate gland, neck of the bladder, cervix of the uterus, and upper vagina. Others relay in microscopic ganglia in or near the walls of seminal vesicles, deferent ducts, epididymis, and uterine tubes. There are no ganglia within the substance of the testes and ovaries. Inconclusive evidence suggests that parasympathetic fibers reach the outer parts of the uterine tubes by passing through the celiac plexus into the superior ovarian nerves that help to supply the oviducts. Histochemical studies indicate that parasympathetic innervation of the genital systems in both sexes is less abundant than sympathetic innervation.

Afferent fibers exist in both the sympathetic and parasympathetic pathways and follow the same routes as the efferent fibers, but in the reverse direction. Their parent pseudounipolar cells are situated in the posterior root ganglia of the lower thoracic, upper lumbar, and midsacral spinal nerves. The peripheral processes of these cells transmit impulses from the genital organs, ducts, and vessels. Their central processes carry the impulses into the cord, where many are carried to the brain in ascending pathways in the lateral and posterior white columns, whereas others form synapses with lateral cornual cells in the related cord segments and are thus involved in spinal reflex arcs.

MALE REPRODUCTIVE ORGANS

The nerves supplying the testis, epididymis, and ductus (vas) deferens are derived from three bilateral sources.

A superior group arises by rootlets from the renal and intermesenteric plexuses, with inconstant contributions from the lumbar splanchnic nerves and the origin of the superior mesenteric plexus. One or two small ganglia are associated with these rootlets. They communicate with the superior ureteric nerves and, on the right side, with branches supplying the duodenum and pancreas. The rootlets coalesce to form two or three slender nerves, which descend on the testicular artery to the testis.

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