Pudendal nerve
Nervus pudendus
Also known as: inferior rectal nerve, perineal nerve, dorsal nerve of penis, dorsal nerve of clitoris, Alcock canal
The main somatic nerve of the perineum (S2–S4). It supplies the external anal and urethral sphincters and the perineal muscles, and carries sensation from the perineum and external genitalia. It is therefore central to continence and sexual function.
Overview
The pudendal nerve arises from the ventral rami of S2, S3 and S4. It leaves the pelvis through the greater sciatic foramen below piriformis. It then hooks around the back of the sacrospinous ligament close to the ischial spine, medial to the internal pudendal artery, and re-enters the perineum through the lesser sciatic foramen. It runs forward in the pudendal (Alcock) canal, a split in the obturator internus fascia on the lateral wall of the ischioanal fossa, with the internal pudendal vessels.
It has three branches:
• the inferior rectal (anal) nerve, to the external anal sphincter and the perianal skin and lower anal canal below the pectinate line;
• the perineal nerve, to the superficial and deep perineal muscles, the external urethral sphincter and the skin of the posterior scrotum or labia;
• the dorsal nerve of the penis or clitoris, the main sensory nerve of the glans.
The pudendal nerve is the somatic (voluntary) partner of the pelvic splanchnic nerves, which arise from the same S2–S4 segments.
- Location
Greater sciatic foramen → around the ischial spine and sacrospinous ligament → lesser sciatic foramen → pudendal canal on the lateral wall of the ischioanal fossa → perineum.
Anatomy
- Innervation
- Motor: the external anal sphincter, the external urethral sphincter, the perineal muscles and part of levator ani.
• Sensory: the perineum, the anal canal below the pectinate line, and the external genitalia (penis or clitoris, posterior scrotum or labia).- Nerve roots
S2, S3, S4.
- Course
Sacral plexus → greater sciatic foramen (infrapiriform) → crosses posterior to the sacrospinous ligament at the ischial spine → lesser sciatic foramen → pudendal (Alcock) canal → inferior rectal, perineal and dorsal nerves.
- Branches
- Inferior rectal nerve: the external anal sphincter, the lower anal canal and the perianal skin.
• Perineal nerve: bulbospongiosus, ischiocavernosus, the superficial and deep transverse perineal muscles, the external urethral sphincter and compressor urethrae, part of levator ani, and the posterior scrotal or labial nerves (skin).
• Dorsal nerve of the penis or clitoris: the skin and glans.
Function
- Voluntary control of urinary and faecal continence (external urethral and anal sphincters)
- Sensation of the perineum and external genitalia
- Sexual function: sensation of the glans, maintenance of erection (ischiocavernosus) and ejaculation (rhythmic contraction of bulbospongiosus)
- Afferent and efferent limbs of the bulbocavernosus and anal wink reflexes (S2–S4)
Clinical significance
Pudendal nerve block
Local anaesthetic is injected near the ischial spine, where the nerve crosses the sacrospinous ligament, through the vaginal wall in obstetrics, with the spine palpated per vaginam. It anaesthetises most of the perineum for the second stage of labour, forceps delivery and episiotomy repair. Additional nerves supply the anterior perineum (ilioinguinal, genitofemoral) and the lateral perineum (posterior femoral cutaneous), so the block may be incomplete.
Stretch injury and pudendal neuralgia
Prolonged or instrumental vaginal delivery can stretch the nerve, contributing to faecal and stress urinary incontinence. Pudendal neuralgia (Alcock canal syndrome) causes burning perineal pain that is worse when sitting and relieved by standing. It is seen in cyclists and after pelvic surgery.
Mnemonics
Roots
"S2, 3, 4 keeps the pelvic floor (and the sphincters) up off the floor."
Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.