The pudendal nerve is the main
nerve
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
of the
perineum
The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), includi ...
.
It carries sensation from the
external genitalia of both sexes and the skin around the
anus
The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
and perineum, as well as the
motor supply to various pelvic muscles, including the
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
or
female external urethral sphincter and the
external anal sphincter
The external anal sphincter (or sphincter ani externus ) is a flat plane of skeletal muscle fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus.
Anatomy
The external anal sphincter measures about 8 ...
. If damaged, most commonly by childbirth, lesions may cause sensory loss or
fecal incontinence
Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is referre ...
. The nerve may be temporarily blocked as part of an
anaesthetic procedure.
The
pudendal canal that carries the pudendal nerve is also known by the eponymous term "Alcock's canal", after
Benjamin Alcock, an Irish anatomist who documented the canal in 1836.
Structure
The pudendal nerve is paired, meaning there are two nerves, one on the left and one on the right side of the body. Each is formed as three roots immediately converge above the upper border of the
sacrotuberous ligament
The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.
Structure
It runs from the sacrum (the lowe ...
and the
coccygeus muscle.
The three roots become two cords when the middle and lower root join to form the lower cord, and these in turn unite to form the pudendal nerve proper just proximal to the
sacrospinous ligament.
The three roots are derived from the
ventral rami
The ventral ramus (pl. ''rami'') (Latin for ''branch'') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami.
Shortly after a spinal ...
of the second, third, and fourth
sacral spinal nerves, with the primary contribution coming from the fourth.
The pudendal nerve passes between the
piriformis muscle and
coccygeus (ischiococcygeus) muscles and leaves the pelvis through the lower part of the
greater sciatic foramen.
It crosses over the lateral part of the
sacrospinous ligament and reenters the pelvis through the
lesser sciatic foramen. After reentering the pelvis, it accompanies the
internal pudendal artery and
internal pudendal vein upwards and forwards along the lateral wall of the
ischiorectal fossa, being contained in a sheath of the
obturator fascia termed the
pudendal canal, along with the internal pudendal blood vessels.
Inside the pudendal canal, the nerve divides into branches, first giving off the
inferior rectal nerve
The Inferior rectal nerves (inferior anal nerves, inferior hemorrhoidal nerve) usually branch from the pudendal nerve but occasionally arises directly from the sacral plexus; they cross the ischiorectal fossa along with the inferior rectal artery a ...
, then the
perineal nerve, before continuing as the
dorsal nerve of the penis (in males) or the
dorsal nerve of the clitoris (in females).
Nucleus
The nerve is a major branch of the
sacral plexus,
with fibers originating in
Onuf's nucleus in the
sacral region of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
.
Variation
The pudendal nerve may vary in its origins. For example, the pudendal nerve may actually originate in the
sciatic nerve
The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals which is the largest branch of the sacral plexus and runs alongside the hip joint and down the lower limb. It is the longest and widest ...
. Consequently, damage to the sciatic nerve can affect the pudendal nerve as well. Sometimes
dorsal rami of the first
sacral nerve
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into t ...
contribute fibers to the pudendal nerve, and even more rarely .
Function
The pudendal nerve has both motor and sensory functions. It does not carry
parasympathetic
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...
fibers but does carry
sympathetic fibers.
The pudendal nerve supplies sensation to the
penis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
in males, and to the
clitoris
The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the op ...
in females, which travels through the branches of both the
dorsal nerve of the penis and the
dorsal nerve of the clitoris.
The posterior
scrotum
The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...
in males and the
labia in females are also supplied, via the
posterior scrotal nerves (males) or
posterior labial nerves (females). The pudendal nerve is one of several nerves supplying sensation to these areas.
[, page=Neurovascular Bundles of the Perineum] Branches also supply sensation to the
anal canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segme ...
.
By providing sensation to the penis and the clitoris, the pudendal nerve is responsible for the
afferent component of
penile erection and
clitoral erection. It is also responsible for
ejaculation
Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compo ...
.
Branches also
innervate
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
muscles of the
perineum
The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), includi ...
and the
pelvic floor; namely, the
bulbospongiosus
The bulbospongiosus muscle (bulbocavernosus in older texts) is one of the superficial muscles of the perineum. It has a slightly different origin, insertion and function in males and females. In males, it covers the bulb of the penis. In fem ...
and the
ischiocavernosus muscles respectively
, the
levator ani
The levator ani is a broad, thin muscle group, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis.
It is attached to the inner surface of each side of the ...
muscle (including the
Iliococcygeus,
pubococcygeus,
puborectalis and either
pubovaginalis in females or
puboprostaticus in males)
the
external anal sphincter
The external anal sphincter (or sphincter ani externus ) is a flat plane of skeletal muscle fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus.
Anatomy
The external anal sphincter measures about 8 ...
(via the inferior anal branch),
and
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
or
female external urethral sphincter.
As it functions to innervate the external urethral sphincter it is responsible for the tone of the sphincter mediated via
acetylcholine
Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...
release. This means that during periods of increased acetylcholine release the
skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...
in the external urethral sphincter contracts, causing urinary retention. Whereas in periods of decreased acetylcholine release the skeletal muscle in the external urethral sphincter relaxes, allowing voiding of the bladder to occur. (Clarification: Unlike the internal sphincter muscle, the external sphincter is made of skeletal muscle, therefore it is under voluntary control of the
somatic nervous system.)
Clinical significance
Anesthesia
A
pudendal nerve block Pudendal anesthesia, also known as a pudendal block, or saddle block, is a form of local anesthesia commonly used in the practice of obstetrics to relieve pain during the delivery of baby by forceps. The pudendal nerve block prevents fainting during ...
, also known as a ''saddle nerve block'', is a
local anesthesia
Local anesthesia is any technique to induce the absence of sensation in a specific part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It ...
technique used in an
obstetric
Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a ...
procedure to anesthetize the perineum during
labor
Labour or labor may refer to:
* Childbirth, the delivery of a baby
* Labour (human activity), or work
** Manual labour, physical work
** Wage labour, a socioeconomic relationship between a worker and an employer
** Organized labour and the la ...
. In this procedure, an anesthetic agent such as
lidocaine
Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, lid ...
is injected through the inner wall of the
vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
about the pudendal nerve.
Damage
The pudendal nerve can be compressed or stretched, resulting in temporary or permanent
neuropathy
Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or o ...
. Irreversible nerve injury may occur when nerves are stretched by 12% or more of their normal length.
If the pelvic floor is over-stretched, acutely (e.g. prolonged or difficult childbirth) or chronically (e.g. chronic straining during
defecation
Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging f ...
caused by
constipation
Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel moveme ...
), the pudendal nerve is vulnerable to stretch-induced neuropathy.
Pudendal nerve entrapment, also known as ''Alcock canal syndrome'', is very rare and is associated with professional
cycling
Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from ...
. Systemic diseases such as
diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
and
multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This ...
can damage the pudendal nerve via
demyelination or other mechanisms.
A pelvic tumor (most notably a large
sacrococcygeal teratoma
Sacrococcygeal teratoma (SCT) is a type of tumor known as a teratoma that develops at the base of the coccyx (tailbone) and is thought to be primarily derived from remnants of the primitive streak. Sacrococcygeal teratomas are benign 75% of the t ...
), or surgery to remove the tumor, can also cause permanent damage.
Unilateral pudendal nerve neuropathy inconsistently causes
fecal incontinence
Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is referre ...
in some, but not others. This is because crossover innervation of the external anal sphincter occurs in some individuals.
Imaging
The pudendal nerve is difficult to visualize on routine
CT or
MR imaging, however under CT guidance, a needle may be placed adjacent to the pudendal
neurovascular bundle A neurovascular bundle is a structure that binds nerves and veins (and in some cases arteries and lymphatics) with connective tissue so that they travel in tandem through the body.
Structure
There are two types of neurovascular bundles: superficia ...
. The
ischial spine, an easily identifiable structure on
CT, is used as the level of injection. A spinal needle is advanced via the
gluteal muscles and advanced within several millimeters of the ischial spine. Contrast (X-ray dye) is then injected, highlighting the nerve in the canal and allowing for confirmation of correct needle placement. The nerve may then be injected with
cortisone
Cortisone is a pregnene (21-carbon) steroid hormone. It is a naturally-occurring corticosteroid metabolite that is also used as a pharmaceutical prodrug; it is not synthesized in the adrenal glands. Cortisol is converted by the action of the enz ...
and local anesthetic to confirm and also treat chronic pain of the external genitalia (known as
vulvodynia in females), pelvic and anorectal pain.
Nerve latency testing
The time taken for a muscle supplied by the pudendal nerve to contract in response to an electrical stimulus applied to the sensory and motor fibers can be quantified. Increased conduction time (terminal motor latency) signifies damage to the nerve.
2 stimulating electrodes and 2 measuring electrodes are mounted on the examiner's gloved finger ("St Mark's electrode").
History
The term pudendal comes from
Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
', meaning external genitals, derived from , meaning "parts to be ashamed of". The
pudendal canal is also known by the eponymous term "Alcock's canal", after
Benjamin Alcock, an Irish anatomist who documented the canal in 1836. Alcock documented the existence of the canal and pudendal nerve in a contribution about
iliac arteries in
Robert Bentley Todd's "The Cyclopaedia of Anatomy and Physiology".
Additional images
File:Gray829.png, The male pelvis, showing the pudendal nerve (centre right)
File:Grant 1962 214.png, Schematic showing the structures innervated by the pudendal nerve
File:Grant 1962 215.png, Diagram of the course of the pudendal nerve in the male pelvis
See also
*
Neurogenic bladder
References
External links
* - "Inferior view of female perineum, branches of the internal pudendal artery."
*
*
*
Diagnosis and treatment at www.nervemed.com www.pudendal.com
{{good article
Nerves of the lower limb and lower torso
Sexual anatomy