Levator ani is a wide thin sheet of muscle, situated on the side of pelvis. It unites with its fellow of the opposite side to form greater part of the pelvic floor.
The muscle has a linear origin, which is quite extensive and comprises of the following structures:
- Back of the body of pubis
- Tendinous arch, which is formed by thickening of fascia covering the obturator internus muscle
- Spine of ischium
From the extensive origin described above, the fibers sweep downward and medially to their insertion in three groups.
- Anterior fibers:
The anterior fibers form the levator prostatae in males and sphincter vaginae in females. They form a sling around the prostate or vagina respectively and are inserted the perineal body, in front of the anal canal.
The levator prostate, which is present in males supports the prostate gland and stabilizes the perineal body. The sphincter vaginae, which is present in females, constricts the vagina and stabilizes the perineal body.
- Intermediate fibers:
These fibers form the puborectalis and pubococcygeus parts of the levator ani. Puborectalis is in the form of a sling lying around the junction of rectum and anal canal. Pubococcygeus passes posteriorly towards the coccyx and is inserted into a small fibrous mass called the anococcygeal body. The anococcygeal body lies between the tip of coccyx and anal canal.
- Posterior fibers:
Posterior fibers form the iliococcygeus part of the muscle. It is inserted into the anococcygeal body and the coccyx.
Levator ani muscle is innervated by the perineal branch of the fourth sacral nerve. It also receives nerve fibers from the perineal branch of pudendal nerve.
The levatores ani of the two sides collectively form an efficient muscular support for pelvic viscera and thus helps them stay in position. The sling-like and sphincter-like portions of the muscle have important role in continence. In addition, it also resists the rise in intra-pelvic pressure during the staining and expulsive efforts of the abdominal muscles.