Gross Anatomy - Nerve Supply to the Pelvis

• Is formed by the fourth and fifth lumbar ventral rami (the lumbosacral trunk) and the first four sacral ventral rami.
• Lies largely on the internal surface of the piriformis muscle in the pelvis.

1. Superior gluteal nerve (L4S1)

• Leaves the pelvis through the greater sciatic foramen above the piriformis.
• Innervates the gluteus medius, gluteus minimus, and tensor fascia lata muscles.

2. Inferior gluteal nerve (L5S2)

• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Innervates the gluteus maximus muscle.

3. Sciatic nerve (L4S3)

• Is the largest nerve in the body and is composed of peroneal and tibial parts.
• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Enters the thigh in the hollow between the ischial tuberosity and the greater trochanter of the femur.

4. Nerve to the obturator internus muscle (L5S2)

• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Enters the perineum through the lesser sciatic foramen.
• Innervates the obturator internus and superior gemellus muscles.

5. Nerve to the quadratus femoris muscle (L5S1)

• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Descends deep to the gemelli and obturator internus muscles and ends in the deep surface of the quadratus femoris, supplying the quadratus femoris and the inferior gemellus muscles.

6. Posterior femoral cutaneous nerve (S1S3)

• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Lies alongside the sciatic nerve and descends on the back of the knee.
• Gives rise to several inferior cluneal nerves and perineal branches.

7. Pudendal nerve (S2S4)

• Leaves the pelvis through the greater sciatic foramen below the piriformis.
• Enters the perineum through the lesser sciatic foramen and the pudendal canal in the lateral wall of the ischiorectal fossa.
• Its branches are described in the section on the nerves of the perineal region.

8. Branches distributed to the pelvis

• Include the nerve to the piriformis muscle (S1S2), the nerves to the levator ani and coccygeus muscles (S3S4), the nerve to the sphincter ani externus muscle, and the pelvic splanchnic nerves (S2S4).

1. Superior hypogastric plexus

• Is the continuation of the aortic plexus below the aortic bifurcation and receives the lower two lumbar splanchnic nerves.
• Lies behind the peritoneum, descends in front of the fifth lumbar vertebra, and ends by bifurcation into the right and left hypogastric nerves in front of the sacrum.
• Contains preganglionic and postganglionic sympathetic fibers, visceral afferent fibers, and few, if any, parasympathetic fibers, which may run a recurrent course through the inferior hypogastric plexus.

2. Hypogastric nerve

• Is the lateral extension of the superior hypogastric plexus and lies in the extraperitoneal connective tissue lateral to the rectum.
• Provides branches to the sigmoid colon and the descending colon.
• Is joined by the pelvic splanchnic nerves to form the inferior hypogastric or pelvic plexus.

3. Inferior hypogastric (pelvic) plexus

• Is formed by the union of hypogastric, pelvic splanchnic, and sacral splanchnic nerves and lies against the posterolateral pelvic wall, lateral to the rectum, vagina, and base of the bladder.
• Contains pelvic ganglia , in which both sympathetic and parasympathetic preganglionic fibers synapse. Hence, it consists of preganglionic and postganglionic sympathetic fibers, preganglionic and postganglionic parasympathetic fibers, and visceral afferent fibers.
• Gives rise to subsidiary plexuses, including the middle rectal plexus, uterovaginal plexus, vesical plexus, differential plexus, and prostatic plexus.

4. Sacral splanchnic nerves

• Consist primarily of preganglionic sympathetic fibers that come off the chain and synapse in the inferior hypogastric (pelvic) plexus.

5. Pelvic splanchnic nerves (nervi erigentes)

• Arise from the sacral segment of the spinal cord (S2S4) and are the only splanchnic nerves that carry parasympathetic fibers. (All other splanchnic nerves are sympathetic.)
• Contribute to the formation of the pelvic (or inferior hypogastric) plexus, and supply the descending colon, sigmoid colon, and other viscera in the pelvis and perineum.