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Pudendal nerve

Recommended video: Sacral plexus [24:26]
The anatomy of the sacral plexus, including its spinal roots and its branches to the pelvis and lower limb.

The pudendal nerve (S2-S4) is a mixed nerve mainly in charge of the sensory and motor supply of the perineum and external genitalia in both sexes. The nerve arises in the pelvic cavity from the sacral plexus, more specifically from the anterior rami of spinal nerves S2, S3 and S4. It leaves the pelvic cavity through the greater sciatic foramen, hooks around the ischial spine enters the perineum through the lesser sciatic foramen.

The main function of the pudendal nerve is to provide sensory supply to the external genitalia in both sexes and the skin around the anus, anal canal and perineum. It also provides motor supply for various pelvic muscles, the external urethral sphincter and the external anal sphincter.

This article will discuss the anatomy and function of the pudendal nerve.

Key facts about the pudendal nerve
Origin Sacral plexus (S2-S4)
Branches Inferior anal (rectal) nerve
Perineal nerve
Dorsal nerve of the penis/clitoris
Supply Skin, organs, and muscles of the perineum and external genitalia in both sexes
  1. Origin and course
  2. Branches and innervation
    1. Inferior anal nerve
    2. Perineal nerve
    3. Dorsal nerve of the penis/clitoris
  3. Clinical relations
    1. Pudendal nerve entrapment syndrome
    2. Pudendal nerve block
  4. Sources
+ Show all

Origin and course

The pudendal nerve is one of the two main branches that originate from the sacral plexus, along with the sciatic nerve. It arises in the pelvis close to the upper border of the sacrotuberous ligament and ischiococcygeus muscle. The nerve courses inferiorly and leaves the pelvis through the greater sciatic foramen. After passing through the foramen, the nerve courses through the gluteal region, running dorsal to the sacrospinous ligament and medial to the internal pudendal vessels.

Accompanied by the internal pudendal artery and vein, and the nerve to the obturator internus, the pudendal nerve passes through the lesser sciatic foramen and into the pudendal canal (Alcock canal). The pudendal artery, vein and nerve are collectively referred to as the pudendal neurovascular bundle.

Upon entering the canal, the pudendal nerve gives rise to the inferior anal nerve (also called the inferior rectal nerve) that provides innervation for the external anal sphincter and the perianal skin. When it reaches the distal portion of the canal, the nerve bifurcates and gives rise to two more branches: the perineal nerve and the dorsal nerve of the penis/clitoris.

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Branches and innervation

The pudendal nerve gives off three branches:

  • Inferior anal nerve
  • Perineal nerve
  • Dorsal nerve of the penis/clitoris

Inferior anal nerve

The inferior anal nerve (also known as the inferior rectal nerve or inferior hemorrhoidal nerve) is usually the first of three branches of the pudendal nerve. While in some individuals it can arise directly from the sacral plexus, it typically branches from the pudendal nerve in the Alcock's canal.

Upon arising, it exits the canal and traverses through the fat of the ischioanal fossa to reach the lateral aspect of the anal canal. The inferior anal nerve is a mixed nerve that provides sensory supply to the inferior portion of the anal canal (to the pectinate line) and the circumanal skin, and motor supply to the external anal sphincter. In addition, the inferior anal nerve may provide sensory innervation to the lower part of the vagina in females.

Perineal nerve

The perineal nerve is the second and the largest of the three branches of the pudendal nerve. It typically arises in the last portion of the Alcock's canal, or just as the pudendal nerve exits the canal. The perineal nerve bifurcates into deep (muscular) and superficial (cutaneous) perineal nerves.

  • The deep branch supplies the muscles of the urogenital triangle (bulbospongiosus, ischiocavernosus and superficial transverse perineal muscle), the external urethral sphincter and the anterior parts of the external anal sphincter and levator ani.
  • The superficial branch provides sensory supply to the posterior scrotal area in males, and the labia minora, vaginal vestibule, lower one-fifth of the vaginal canal and the posterior aspect of the labia majora and in females.

Dorsal nerve of the penis/clitoris

The dorsal nerve of the penis/clitoris is considered to be the terminal branch of the pudendal nerve. The dorsal nerve of the penis/clitoris is the sole sensory supplier of the external genitalia, thus it is crucial in maintaining normal sexual function. More specifically, in males, this nerve innervates the skin over the shaft of the penis, the prepuce, and the glans of the penis. In females, the dorsal nerve of the clitoris innervates the clitoral body and the glans.

To summarize, the pudendal nerve supplies the skin, organs, and muscles of the perineum; therefore, it is in charge of micturition, defecation, erection, ejaculation, and, in the female, parturition.

Take a quiz about the sacral plexus to test your knowledge on this important topic.

If you want to know more about the sacral plexus and its nerves, check out our study unit:

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