Pudendal Nerve (S2 – S4)
The pudendal nerve (AB1) leaves the pelvis through the infrapiriform foramen (AB2), extends dorsally around the sciatic spine (AB3) and passes through the lesser sciatic foramen (AB4) into the ischioanal fossa. It then runs along the lateral wall of the fossa within the pudendal canal (Alcock’s canal) to below the symphysis, sending its terminal branch to the dorsal side of the penis or cli-toris, respectively.
Numerous branches are given off in the pu-dendal canal; the inferior rectal nerves (A – C5), which may also originate directly from the second to fourth sacral nerves, penetrate through the wall of the canal to the perineum and supply motor fibers to the external sphincter muscle of anus (AB6) and sensory fibers to the skin around the anus as well as the lower two-thirds of the anal canal.
The perineal nerves (AB7) subdivide into deep and superficial branches. The deep branches participate in the innervation of the external sphincter muscle of the anus. More superficially, they supply the bulbo-cavernous muscle, the ischiocavernous muscle, and the superficial transverse per-ineal muscle. The superficial branches supply sensory fibers to the posterior part of the scrotum (posterior scrotal nerves) (AC8) in males and to the labia majora (posterior labial nerves) (BC9) in females. They also supply the mucosa of the urethra and the bulb of penis in males, and the external urethral opening and the vestibule of vagina in females.
The terminal branch, the dorsal nerve of thepenis (A10) or dorsal nerve of the clitoris (B11),respectively, sends motor branches to the deep transverse perineal muscle, the deep sphincter muscle, and the sphincter muscle of urethra (B12). After passing through the urogenital diaphragm (AB13), it gives off a branch to the cavernous body of the penis in males, and to the cavernous body of the cli-toris in females. In males, the nerve runs along the dorsum of the penis and gives offsensory branches to the skin of the penis and the glans. In females, it supplies sensory fibers to the clitoris including the glans.
The levator ani muscle and the coccygeal muscle are supplied directly by nerve branches from the sacral plexus.
The anterior branches of the fourth and fifth sacral nerves form a fine plexus on the coccygeal muscle, the coccygeal plexus (AB14). The anococcygeal nerves originate from here; they supply sensory fibers to the skin over the coccyx and between coccyx and anus (C14).