Pubo-analis muscle

At a glance

English

Pubo-analis muscle

Latin (TA2)

Musculus puboanalis

System

Muscle

Region

Trunk

Side

Paired, left and right

About the pubo-analis muscle

Levator ani, the main muscle of the pelvic floor, is made up of several groups of fibres named after where they begin and end. The pubo-analis, or puboanal muscle, is one of the medial groups of the pubococcygeus part. Its fibres leave the back of the pubic bone, pass backward beside the midline and end on the wall of the anal canal, where they mix with the anal sphincters.

The fibres arise from the inner surface of the body of the pubis, close to the pubic symphysis, alongside the other pubococcygeal fibres. They run backward on each side of the gap in the pelvic floor through which the urethra and rectum pass, the levator hiatus. On reaching the junction between rectum and anal canal, they turn downward and insert into the groove between the internal and external anal sphincters, joining the longitudinal muscle layer of the canal and the fibres of the external sphincter. Puborectalis lies just lateral and below, forming its familiar sling behind the anorectal junction.

By pulling the anal canal forward and upward towards the pubis, the pubo-analis helps to lift and support the anorectal region. With puborectalis it sharpens the angle between rectum and anal canal and with the sphincters it helps to keep the canal closed, so it plays a part in continence. It also shares in the general work of the pelvic floor in supporting the pelvic organs whenever pressure inside the abdomen rises.

Its nerve supply comes from the nerve to levator ani, from the third and fourth sacral segments, and from branches of the pudendal nerve, especially the inferior rectal nerve. Blood reaches it through branches of the internal iliac artery, mainly the inferior rectal and internal pudendal arteries. Damage to this region of the pelvic floor by stretching or surgery can weaken the support of the anal canal and contribute to incontinence.

Attachments, action and supply

Origin

Inner surface of the body of the pubis, near the pubic symphysis.

Insertion

Intersphincteric groove of the anal canal, blending with the longitudinal muscle and external anal sphincter.

Action

Lifts the anal canal forward and upward and helps to close it, aiding continence and pelvic floor support.

Nerve supply

Nerve to levator ani (S3, S4) and the inferior rectal branch of the pudendal nerve.

Blood supply

Inferior rectal and internal pudendal arteries, branches of the internal iliac system.