The pelvic floor (also known as pelvic diaphragm) is the region of the human body which lies below the peritoneum and holds up the urogenital system. It is bounded anteriorly by the pubis, posteriorly by the sacrum, and laterally by the iliac and ischial portion of the pelvis. Histologically, the pelvic floor is formed by a series of small and flat skeletal muscles and fasciae. They are: the right and left levator ani, the right and left coccygeus, the sphincter ani externus, the deep transverse perineal, the superficial transverse perineal, ischiocavernosus, and the the sphincter urethrae muscle, and fasciae.
Muscles of the pelvic floor
Levator ani muscle: It is triangular and consists of two smaller muscles: a) the pubococcygeus and b) the iliococcygeus; together with the fasciae, they form a funnel-shaped muscular sheet which descends to the anus. The pubococcygeus arises from the internal surface of the pubic rami and is inserted into the anococcygeal body and the anterior sacrococcygeal ligament. The iliococcygeus muscle originates from the tendinous arch, then runs backwards to be inserted into the coccyx below the pubococcgeus muscle. Action: the lavator ani muscle raises the floor of the pelvis, making it more resilient and firmer.
Coccygeus muscle: It is also triangular in shape and it is located on the inner surface of the sacrospinous ligament. It arises from the ischial spine and its wide base is inserted into the lateral borders of the lower sacral and the coccygeal vertebrae. The anterior border of the muscle adjoins the posterior border of the levator ani muscle to form a continuous muscular sheet.
Sphincter ani externus muscle: It is an unpaired muscle that embraces the perineal (anal) part of the rectum. It originates from the posterior surface and apex of the coccyx and is inserted into the central tendon of the perineum. Action: contraction of the muscle compresses the anus from the sides and makes it slit-like.
Deep transverse perineal muscle: It is a paired muscle that arises from the ischial tuberosities and is inserted into the perineal body. Action: it provides support for the perineum and the pelvic diaphragm. In males, it also gives support to the bulb of the penis.
Superficial transverse perineal muscle: It is inconstant, sometimes absent. It is situated at the posterior border of the urogenital diaphragm, arising from the ramus of ischium of pelvis and is inserted into the central tendon of perineum.
Ischiocavernosus muscle: it is a muscle of the urogenital triangle. It arises from the ramus of ischium and is inserted into the corpus cavernosus penis, or clitoridis in females. Action: compresses the crux of the penis or clitoris. Nerve supply: pudendal.
Sphincter urethrae muscle: It is a paired muscle that lies in front of the deep perineal muscle. It originates from the pubic ramus and is inserted into the median raphe. Action: it compresses the urethra as well as the bulbourethral glands in the male and the greater vestibular glands in the female.
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| Pelvic floor muscles. The coccygeus muscle cannot be seen as it is hidden behind the deep transverse perineal. |
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