pudendal nerve

The pudendal nerve arises from the sacral plexus (ventral rami of S2-S4) and exits the pelvis through the greater sciatic foramen, travels around the ischial spine and sacrospinous ligament, and re-enters via the lesser sciatic foramen to run through the pudendal (Alcock's) canal along the lateral wall of the ischioanal fossa. It gives rise to three main branches: the inferior rectal nerve (innervates external anal sphincter, motor and sensory to lower anal canal), perineal nerve (innervates most perineal muscles, posterior scrotum/labia), and dorsal nerve of the penis/clitoris (sensory).

Functionally, it provides: (1) Motor innervation to external anal sphincter, external urethral sphincter, bulbospongiosus, ischiocavernosus, and other perineal muscles - critical for voluntary control of urination and defecation, and for the male ejaculatory reflex. (2) Sensory innervation to the skin of the perineum, scrotum/labia majora, and penis/clitoris. (3) Parasympathetic contribution to erectile function via cavernous nerves (though erection is primarily mediated by pelvic splanchnic nerves S2-S4).

Clinical relevance: Pudendal nerve block is used for pain relief during the second stage of labor and for perineal procedures, targeting the nerve as it passes near the ischial spine. Pudendal nerve injury can occur during childbirth (stretch injury), chronic cycling, or pelvic surgery, leading to fecal/urinary incontinence or erectile dysfunction. Pudendal neuralgia presents as chronic perineal pain, often worse with sitting (due to nerve entrapment in Alcock's canal) and relieved by standing or sitting on a toilet seat. Understanding the nerve's course through the greater and lesser sciatic foramina is essential for surgical approaches and nerve blocks.