Anatomy chapters
Muscles of the pelvic floor
The pelvic diaphragm (levator ani and coccygeus), its parts, nerve supply and openings, the perineal body, and why childbirth damage causes prolapse and incontinence.
- The pelvic floor (pelvic diaphragm) is formed by levator ani and coccygeus.
- Levator ani has three parts: puborectalis, pubococcygeus and iliococcygeus; puborectalis keeps the anorectal angle for continence.
- It is supplied by S4 and the pudendal nerve (S2–S4); damage in childbirth leads to prolapse and stress incontinence.
On this page
Overview
The pelvic floor is a muscular sheet that closes the bottom of the pelvic cavity. It is shaped like a funnel or hammock.
It supports the pelvic organs, resists rises in abdominal pressure (coughing, straining) and helps control urine and faeces.
It is pierced by the urethra, the anal canal and, in women, the vagina.
The pelvic diaphragm
The pelvic diaphragm is made of two muscles on each side:
- Levator ani (the larger, front part).
- Coccygeus (the smaller, back part).
They are covered above and below by fascia.
Levator ani
Attachments
- Origin: the back of the body of the pubis, the tendinous arch of the obturator fascia (a thickening over obturator internus) and the ischial spine.
- Insertion: the perineal body, the anococcygeal body (ligament), the walls of the organs passing through it, and the coccyx.
Parts
| Part | Fibres | Main role |
|---|---|---|
| Puborectalis | Loop from the pubis around the back of the anorectal junction | Keeps the anorectal angle; key for faecal continence |
| Pubococcygeus | From the pubis back to the anococcygeal body and coccyx | Main part of the muscle; supports organs. In women its medial fibres (pubovaginalis) help support the vagina; in men (levator prostatae) the prostate |
| Iliococcygeus | From the tendinous arch and ischial spine to the anococcygeal body and coccyx | Thin back part; supports the pelvic organs |
Puborectalis forms a U-shaped sling that pulls the anorectal junction forward and keeps the anorectal angle. It relaxes during defecation to straighten the angle.
Puborectalis does not attach to the coccyx. It forms a sling around the anorectal junction with both ends on the pubis.
Nerve supply
- Nerve to levator ani from the ventral ramus of S4, on its upper surface.
- Branches of the pudendal nerve (S2–S4), on its lower surface (inferior rectal and perineal nerves).
Actions
- Supports the pelvic organs and resists rises in pressure.
- Helps keep continence of urine and faeces.
- Helps the fetal head rotate forward in labour.
Coccygeus
A small triangular muscle from the ischial spine to the side of the lower sacrum and coccyx. It lies on the sacrospinous ligament.
It is supplied by S4 and S5 and helps support the pelvic organs.
Openings in the pelvic floor
The levator ani of the two sides leave a gap at the front, the urogenital hiatus, through which pass:
- The urethra (both sexes).
- The vagina (in women).
Further back, the anal canal passes through the floor.
The perineal body
The perineal body is a mass of fibromuscular tissue between the anal canal and the vagina (or bulb of the penis).
Many muscles attach to it: levator ani, the external anal sphincter, bulbospongiosus, and the superficial and deep transverse perineal muscles.
The perineal body is the "central tendon of the perineum". If it is torn in childbirth and not repaired, the pelvic floor weakens and prolapse may follow.
The urogenital diaphragm and perineum
Below the pelvic floor lies the perineum, a diamond-shaped region divided into the urogenital triangle in front and the anal triangle behind.
In the urogenital triangle, the deep perineal pouch contains the external urethral sphincter and the deep transverse perineal muscles. The strong perineal membrane forms its lower surface.
On each side of the anal canal lies the fat-filled ischioanal (ischiorectal) fossa. Infection here spreads easily and can cross behind the anal canal to the other side (horseshoe abscess).
Clinical relevance
Damage in childbirth
How it happens: a long or difficult labour, a large baby or instrumental delivery stretches or tears levator ani, the perineal body or the pudendal nerve.
What you see: a weak pelvic floor later in life, leading to prolapse and incontinence.
Uterine and vaginal prolapse
How it happens: weakness of the pelvic floor and the ligaments that hold the uterus and vagina (especially the cardinal and uterosacral ligaments).
What you see: a feeling of something coming down. The bladder can bulge into the front vaginal wall (cystocele) and the rectum into the back wall (rectocele).
Stress urinary incontinence
How it happens: weak support of the bladder neck and urethra.
What you see: leaking of urine on coughing, sneezing or lifting. Pelvic floor exercises strengthen levator ani and help many women.
Episiotomy
How it happens: a planned cut to enlarge the vaginal opening during delivery.
What you see: a mediolateral cut is usually made, angled away from the midline, to avoid extending into the perineal body and external anal sphincter.
A tear or cut that reaches the external anal sphincter risks faecal incontinence if it is not recognised and repaired.
Pudendal nerve block
Local anaesthetic is injected near the ischial spine, where the pudendal nerve crosses it, to numb the perineum during delivery.
Expect: the muscles forming the pelvic diaphragm, the attachments and parts of levator ani, the role of puborectalis in continence, the nerve supply (S4 and pudendal), the perineal body as the central tendon, the landmark for a pudendal block and why episiotomy is mediolateral.
Quick revision
- Pelvic diaphragm: levator ani + coccygeus.
- Levator ani: from pubis, tendinous arch and ischial spine.
- Parts: puborectalis (continence sling), pubococcygeus, iliococcygeus.
- Nerve supply: S4 and branches of the pudendal nerve (S2–S4).
- Perineal body: central tendon of the perineum.
- Weak floor: prolapse, cystocele, rectocele, stress incontinence.
- Pudendal block: near the ischial spine.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
Which muscles form the pelvic floor?
Levator ani and coccygeus, which together form the pelvic diaphragm.
What is the role of puborectalis?
It forms a sling around the anorectal junction and keeps the anorectal angle, which helps faecal continence.
What is the perineal body?
A fibromuscular mass between the anal canal and the vagina or penis where many perineal muscles attach.
Which nerve supplies levator ani?
The nerve to levator ani from S4, and branches of the pudendal nerve.