The Pudendal Nerve

Key points

• • The pudendal nerve arises from the sacral plexus (roots S2, S3 and S4), the roots summarised as 'S2, 3 and 4 keep the pelvis off the floor'.
• • It leaves the pelvis through the greater sciatic foramen, hooks around the ischial spine, and enters the perineum through the lesser sciatic foramen.
• • In the perineum it runs in a sheath of fascia on the side wall, the pudendal (Alcock's) canal, together with the internal pudendal vessels.
• • It supplies the skin of the perineum and external genitals and the perineal muscles, including the external anal and urethral sphincters, while much of the levator ani is supplied directly by sacral plexus branches.
• • Because it controls the external sphincters, it gives voluntary control over passing urine and faeces.
• • It can be numbed where it hooks around the ischial spine (a pudendal nerve block) to ease pain in the birth canal during childbirth.