The nerve to levator ani arises directly from the anterior rami of S3 and S4 (sometimes S5) and runs on the upper (pelvic) surface of the levator ani muscle. It is the main motor nerve of the pelvic floor, supplying iliococcygeus and pubococcygeus, including the puborectalis part. Some fibres to the levator ani also arrive through branches of the pudendal nerve from below.
| Origin | Anterior rami of S3 and S4, sometimes S5 |
|---|---|
| Course | Runs forward on the superior (pelvic) surface of levator ani, entering the muscle from above |
| Motor | |
| Sensory |
|
This nerve lies on the pelvic floor and can be stretched during vaginal delivery as the fetal head descends, contributing to pelvic floor weakness, pelvic organ prolapse and urinary or faecal incontinence. It can also be injured during deep pelvic surgery such as rectal cancer resection or sacrospinous fixation. Pelvic floor muscle training aims to strengthen muscles supplied by this nerve.
Stretching of the nerve during vaginal birth weakens levator ani, widening the gap the pelvic organs rest on and predisposing to prolapse and stress incontinence years later.
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