Pudendal nerve

The pudendal nerve is a nerve in the pelvic region that innervates the external genitalia of both sexes, as well as sphincters for the bladder and the rectum.

Anatomy
The pudendal nerve originates in the sacral plexus; it derives its fibers from the ventral branches of the second, third, and fourth sacral nerves (S2, S3, S4).

It passes between the piriformis and coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen.

It crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen.

It accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal.

The pudendal nerve gives off the inferior rectal nerves. It soon divides into two terminal branches: the perineal nerve, and the dorsal nerve of the penis (males) or the dorsal nerve of the clitoris (in females).

Physiology
The pudendal nerve innervates the penis and clitoris, bulbospongiosus and ischiocavernosus muscles, and areas around the scrotum, perineum, and anus. At sexual climax, the spasms in the bulbospongiosus and ischiocavernous results in ejaculation in the male and most of the feelings of orgasm in both sexes.

Pathology
Difficult childbirth or bicycling can compress or stretch the pudendal nerve, causing temporary loss of function, but permanent injury is rare. Entrapment of the nerve is very rare but can happen. A pelvic tumor (most notably a large sacrococcygeal teratoma), or surgery to remove the tumor, can damage this nerve permanently.