Origin
Anococcygeal raphe, perineal muscles.
Insertion
Coccyx, anococcygeal ligament, perineal muscles.
Blood supply
Internal pudendal artery.
Nerve supply
S4 pudendal nerve.
Action
The external anal sphincter contracts and keeps the anal opening closed. The internal anal sphincter is always in highly contracted stage and helps the external sphincter to close the anal opening. Both these sphincters helps to expel the feces.
Disease/Injury
Obstructed defecation means difficulty in passing feces or constipation can occur if the muscles do not relax properly.
Muscle Exercise
To strengthen the sphincter ani muscles, you need to lift and squeeze your sphincter as if you are avoiding passing gas. Then tighten your muscles as if you are trying to stop your urine in mid flow. Initially start the two exercises separately, then combine them by doing the first one and holding it and then the second movement. Hold this contraction for some time, then relax it completely and start again.
Interesting facts
You can use your external sphincter ani to delay the bowel movements as per your will.
