There are two small muscles in the anus (opening from the rectum) that help to control bowel movements. These muscles are known as internal and external sphincters (sfink-ters). (Figures 1 and 2)
These muscles are normally closed to prevent uncontrolled leakage of bowel movements. To have a bowel movement, these muscles must relax and open at the same time. Anal manometry is a test that studies how these muscles are working.