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Innervation/ Nerve Supply of Levator Ani Muscle/Levator ani is a broad, thin muscle, 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 lesser pelvis, and these unite to form the greater part of the pelvic floor. The coccygeus muscle completes the pelvic floor which is also called the pelvic diaphragm. It supports the viscera in the pelvic cavity and surrounds the various structures that pass through it. The levator ani is the main pelvic floor muscle and painfully contracts during vaginismus. It also contracts rhythmically during orgasm.[rx]
Origin and Insertion of Levator Ani
- The levator ani arises – in front, from the posterior surface of the superior pubic ramus lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia.
- Posteriorly – this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a varying distance above the arch, in some cases reaching nearly as high as the canal for the obturator vessels and nerve.
- The fibers pass downward – and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous ridge called the anococcygeal body or raphe, which extends between the coccyx and the margin of the anus.
- The middle fibers – are inserted into the side of the rectum, blending with the fibers of the sphincter muscles; lastly in the male, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the external anal sphincter and transverse perineal muscles, at the central tendinous point of the perineum.
The anterior portion is occasionally separated from the rest of the muscle by connective tissue. From this circumstance, as well as from its peculiar relationship with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of levator prostate. In the female, the anterior fibers of the levator ani descend upon the side of the vagina.
It is made up of the following three muscles:
- Puborectalis muscle – originates lateral from the symphysis on both sides and encircles the rectum (anorectal junction) which causes a ventral bend between the rectum and anal canal. Partly it is interwoven with the external anal sphincter.
- Pubococcygeus muscle – runs from the pubic bone (lateral of the origin of the puborectalis muscle) to the tendinous center of the perineum, anococcygeal body and tailbone. In men, medial muscle fibers are partly connected to the prostate.
- Iliococcygeus muscle – extends more laterally from the fascia of obturator internus muscle to the tailbone. As a whole, the levator ani builds a V-shaped structure. Both levator arms limit a triangle opening (levator hiatus) which is divided by perirectal fibers into the urogenital hiatus (ventral) and anal hiatus (dorsal). The urogenital hiatus is the pathway for the urethra and, in women, the vagina. The rectum runs through the anal hiatus.
Innervation/ Nerve Supply of Levator Ani Muscle
- The levator ani muscles are mostly innervated by the pudendal nerve, perineal nerve and acting together.
- It is primarily supplied by the nerve to levator ani (S4). To a small degree, the pudendal nerve (S2-S4) contributes to its innervation as well.
Functions of Levator Ani
- The pubococcygeus muscle controls urine flow and contracts during orgasm as well as assisting in male ejaculation.[rx] It also aids in childbirth as well as core stability.[rx]
- A strong pubococcygeus muscle has also been linked to a reduction in urinary incontinence and proper positioning of the baby’s head during childbirth.
- Through its tonic activity, the levator ani stabilizes the abdominal and pelvic organs on the one hand and controls the opening and closing of the levator hiatus on the other hand.
- While in a quiescent state, the urethra and the rectum are mechanically closed at the levator hiatus. The muscle relaxes at the beginning of urination and defecation. By this means the levator ani muscle plays a crucial role in the preservation of urinary and bowel continence.
The Kegel exercises are a series of voluntary contractions of all the perineal muscles. Such movement is done in an effort to strengthen all the striated muscles in the perineum’s area. They are often referred to simply as “Kegels”, named after their founder, Dr. Arnold Kegel.[rx] These exercises also serve to contract, among others, the ischiocavernosus, bulbospongiosus, and cremaster muscle in men, as a voluntary contraction of the pubococcygeus muscle also engages the cremasteric reflex, which lifts the testicles up, although this does not occur in all men. Kegel exercises have been prescribed to ameliorate erectile dysfunction due to venous leakage and to help men control premature ejaculation[rx] and to treat urinary incontinence in both sexes.[rx][rx]