The perineum nerve

The perineum nerve

The perineum is the lowest part of the trunk. In males there are two openings, one of the gastro-intestinal system and the other being the common opening of urinary and genital system. In females there are three separate openings, one each of the gastrointestinal tinal,genital and urinary systems. The perinea body supports the reproductive system. Its injury without repair, may lead to prolapse.of the uterus. Pudenda nerve supplies muscles, skin, mucous membrane of both anal and urogenital triangles. Pudendum means " to be ashamed of ". So far it is the most covered area of the body. Perineum is the region at the lower end of the trunk, in the inter-val between the two thighs. The external genitalia are located, in the perineum. The perineum forms the lower division of the pelvis that lies below the pelvic diaphragm, formed by the levator an and coccyges, and fills in the pelvic outlet or inferior aperture of the pelvis.

Divisions of the perineum               

A transverse line joining the anterior parts of the ischial tuberosities,and passing immediately anterior to the anus,divides the perineum into two triangular areas, a posterior, anal region or triangle, and an anterior, urogenital region or triangle. The anal region contains the termination of the anal canal in the median plane and an ischioanal fossa on each side.Urogenital region contains the external urogenital organs.In males, the urethra enclosed in the root of penis,partly hidden anteriorly by the scrotum; and females, the female external genital organs. In the urogenital region, there are the superficial perineal space or pouch and the deep perineal space or pouch. The chief neurovascular bundle of the perineum occupies a fascial tunnel, the pudendal canal, and contains the pudendal nerve and the internal pudendal vessels. The pudendal canal lies in the lateral wall of the ischioanal fossa.

Dissection :

Clean the sacrotuberous and sacrospinous ligaments identify coccyx in the midline posteriorly and locate the ischial tuberosity.Define the ischiopubic rami till the lower margins of pubic symphysis anteriorly. Identify the openings of urethra, anal canal and vagina if is a female cadaver. Define perineal body in the centre of perineum between vagina and anus.Dissect the parts of external anal sphincter. Pass a forceps downwards and backwards deep to the membranous layer of the superficial fascia of the anterior abdominal wall.In the female,remove the fat from the labium majus and expose the membranous layer.Incise it and expose 
the posterior part of this space and all its contents both in male and female cadavers.Note the posterior limit where the membraus layer passes superiorly to fuse with the perineal membrans. In the male, expose the membranous layer in the perineum. Make an incision membranous layer on the side and dissect the ischiocavernosus, bulbospongiosus and superficial transverse perinel muscles, nerves, blood vessels present in the superficial perineal space. The posterior scrotal/labial vessels and nerves pierce the
posterolateral corner of perineal membrane to enter the superficial perineal space. Identiy the structures piercing the perineal membrane in both male and female. Note the ill-defined nature of the perineal membrane in female as it is pierced by vagina in addition to urethra. Identify the various female external genital organs. Dissect the inferior rectal vessels and nerve and follow them to the lateral wall of the ischioanal fossa.Remove the fat from the ischioanal fossa.Identify and trace the pudendal nerve and vessels in the fascial pudendal canal on the lateral wall of the ishioanal fossa.          

Deep transverse perinei : It forms an incomplete sheet of skeletal muscle extending across the urogenital triamgle from the medial aspects of the ischiopubic rami.Posteriorly,the sheet is attached to perineal body where its fibres decussate with those of opposite Anteriorly, the muscles are deficient and the visceral structures pass across the endopelvic fascia and the perineal membrane. Some fibres pass to the deep part of external anal sphincter posteriorly and sphincter urethrae ( contained within the urethra ).Together with superficial transverse perinei the muscles act to together the perineal body in median plane. The muscle gives dynamic support for pelvic viscera. Supplied by perineal branches of pudenal nerve and vassels.

Distal urethral sphincter machanism : Consists of striated and smooth muscles of urethra and the pubourethralis component of levator ani which surrounds the urethra at the point of maximum concentration of those muscles.It surrounds the membranous urethra in the male. Smooth muscle fibres also reach up to the lowest part of the neck of the bladder and between the two, fibres lie on the surface of prostate. Bulk of fibres surround the membranous urethra. There are circularly disposed striated muscle fibres called
rhabdosphincter which forms main part of distal urethral sphincter mechanism. Some fibres are attached to inner surface of the ischiopubic ramus, forming compressor urethrae.

Pudenda nerve

Pudenda nerve is the chief nerve of the perineum and of the external genitalia. It is accompanied by the internal pudenda vessels. Pudenda nerve arises from the sacral plexus in the pelvis.It is derived from spinal nerve S2, S3, S4. It originates in the pelvis,enters glutamate region through greater sciatic notch, leaves it through lesser sciatic notch to enter the pudenda canal in the lateral wall of ischioanal Foss. It terminates by dividing into branches. In the pelvis, the pudenda nerve descends in front of the reformists deep to its fascia. It leaves the pelvis, to enter the glutamate region, by passing through the lower part of the greater sciatic foreman, between the reformists and the coccyges, medial to internal pudenda vessels. In the glutamate region, the pudenda nerve crosses the apex of the sacrosanctness ligament, under cover of glutenous maximums. Here it lies medial to the internal pudenda vessels which cross the challis spine. Accompanying these vessels, the nerve leaves the glutamate region by passing through the lesser sciatic foreman, and enters the pudenda canal. In the pudenda canal, the neurovascular bundle lies in the lateral wall of the ischioanal. In the posterior part of the pudendal canal the pudendal nerve gives off the inferior rectal nerve, and then divides into two terminal branches, the perineal nerve and the dorsal nerve of the penis or clitoris. The inferior rectal nerve pierces the medial wall of the pudendal canal,  crosses the ischioanal fossa from lateral to medial side, and supplies the external anal sphincter, the skin around the anus, and the lininig of the anal canal below the pectinate line. The perineal nerve is the larger terminal branch of the pudendal nerve.

Internal pudenda artery

This is the chief artery of the perineum and of the external genital organs. It is smaller in females than in males. The artery is the smaller terminal branch of the anterior division of the internal iliac artery,given off in the pelvis; the larger branch is the inferior gluteal. The courseof internal pudendal artery is similar to the course of pudendal nerve. In the pelvis, the artery runs downwards in front of the piriformis, the sacral plexus and the inferior gluteal artery. It leaves the pelvis by piercing the parietal pelvic fascia and passing through the greater sciatic foramen,below the piriformis, thus enterning the glutal region. In the gluteal region,the artery crosses the dorsal aspect of the tip of the ischial spine, under cover of the gluteus maximus. Here it lies between the pudendal nerve medially and the nerve to the obturator internus laterally. It leaves the gluteal region by passing through the lesser sciatic foremen, and thus enters the pudendal canal. In the pudendal canal, the artery runs downwards and forwards in the lateral wall of the ischioanal fossa, about 4 cm above the lower margin of the ischial tuberosity.Here it is related to the dorsal nerve above and the perineal nerve below.
The artery gives off the inferior rectal artery in the posterior part of the canal, and the perineal artery in the anterior part. The internal pudendal artery continues into the deep perineal space as the artery of the penis or of the clitoris. In the deep perineal space, the artery of the penis or clitoris which is continuation of internal pudendal artery, runs forwards close to the side of pubic arch, medial into the dorsal nerve of penis or of clitoris. The artery ends a little behind the arcuate pubic ligament by dividing into the depp and dorsal arteries of penis or of the clitoris.    

Histology of body penis/clitoris : Penis consists of two corpora cavernosa containing the deep artery of the penis and a single corpora spongiosum with the urethra. All three erectile masses contain spaces or caverns. The spaces are larger in corpora are covered by fasciae and skin. In the deep fascia lie deep dorsal vein of panis, two dorsal arteries and two dorsal nerves of penis.The superficial dorsal vein of the penis lies in the superficial fascia. Clitoris comprises two corpora covernosa only. Corpus spongiosum is absent. The two erectile masses contain caverns or spaces.         

Clinical anatomy : The two ischioanal fossae allow distention of the rectum and anal canal during passage of faeces. Both the perianal and ischioanal spaces are common sites of abscesses. Sometimes an abscess may burst into the anal canal or rectum internally, and on to the surface of the perineum externally. In this way an ischioanal type of anorectal fistula or fistula in ano may be produced. The most common site of the internal opening is in the floor of one of the anal crypts. If the abscess bursts only externally, and healing does not follow an external sinus is produced. Through the horseshoe recess a unilateral absces may become
bilateral. The ischioanal fat acts as a cushion-like support to the rectum and anal canal. Loss of this fat in debilitating diseases like diarrhoe in children may result in prolapse of the rectum.