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Muscles of the Pelvic Floor

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The Pelvic Floor

The pelvic floor or pelvic diaphragm is important in providing support for the pelvic organs (e.g. urinary bladder and intestines in men, and additionally the uterus in women), and in the maintenance of continence as part of the urinary and anal sphincters. The pelvic floor muscles are the layer that supports the pelvic organs and spans the bottom of the pelvis.

During birthing, the pelvic floor facilitates movement of the fetus towards the pelvic girdle by resisting the descent of the presenting part, which causes the fetus to rotate forwards and therefore results in a majority of fetuses being born headfirst. The pelvic floor also helps maintain optimal intra-abdominal pressure.

Muscles of the pelvic floor
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Origins, insertions, innervation and functions of the muscles of the pelvic floor.

Pelvic Floor Muscles

  1. Pelvic Diaphragm: Levator ani muscle (Puborectalis, Pubococcygeus and Iliococcygeus) and Coccygeus
  2. Urogenital Diaphragm: Deep transverse perineal, Sphincter urethrae
  3. Sphincters and erectile muscles of the urogenital and intestinal tract: External anal sphincter, Bulbospongiosus, Ischiocavernosus, Superficial transverse perineal

Muscle Layers

  1. Superficial perineal layer (innervated by the pudendal nerve): Bulbocavernosus, Ischiocavernosus, Superficial transverse perineal, External anal sphincter (EAS)
  2. Deep urogenital diaphragm layer (innervated by pudendal nerve): Compressor urethera, Uretrovaginal sphincter, Deep transverse perineal
  3. Pelvic diaphragm (innervated by sacral nerve roots S3-S5): Levator ani [pubococcygeus (pubovaginalis, puborectalis), iliococcygeus, coccygeus/ischiococcygeus], Piriformis, Obturator internus

The pelvic floor muscles span from the tailbone (coccyx) to the pubic bone; front to back, and also side to side. These muscles are normally firm, thick, and resemble a muscular trampoline in its ability to move up and down. Even though the pelvic floor is hidden from view, it can be consciously controlled, moved, and exercised, similar to our arms, legs, or abdominal muscles.

In women, the bladder, uterus and bowel lie on the pelvic floor muscle layer. In addition, there is a hole in the pelvic floor muscle layer for passages to pass through. There 2 of these passages in men (the urethra and anus) and 3 passages in women (the urethra, vagina, and anus). Usually, the pelvic floor muscles can be found tightly wrapped around these holes such that the passages are kept shut. There is an additional circular muscle around the anus (the anal sphincter) and around the urethra (the urethral sphincter) to better maintain a closed state.

Function

The pelvic floor muscles function as support for the organs that lie on it. The sphincters (anal and urethral sphincters) provide conscious control over the bowels and bladder, respectively, such that we are able to control the release of feces/flatus, or urine, and to prevent and delay emptying until convenient.

Upon contraction, pelvic floor muscles will lift upwards the internal organs, and tighten the sphincters openings of the vagina, anus and urethra. Relaxation of the pelvic floor muscles allows for passage of feces and urine.

Additionally, pelvic floor muscles are important for the sexual function of both men and women. In men, these muscles are important for erectile function and ejaculation. In women, voluntary contractions (squeezing) of the pelvic floor muscles contribute to enhanced sexual sensation and arousal. During pregnancy, the pelvic floor muscles in women also provide support for the baby and assisting in birthing.

Finally, another function of the pelvic floor muscles, in conjunction with the abdominal and back muscles, is to help stabilize and support the spine.

Pathology

A weakened pelvic floor often presents due to childbirth, obesity, and the associated straining of chronic constipation. However, corrective surgery can sometimes be avoided by performing pelvic floor exercises designed to improve muscle tone.

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References:

Author:

  • Alice Ferng, MD-PhD

Illustrators:         

  • Pelvic floor muscles - superior view - Liene Znotina 
  • Pelvic floor muscles - inferior view - Liene Znotina 
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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