The relation of sensation in the anal canal to the functional anal sphincter: a possible factor in anal continence.

In normal subjects the length of the functional anal sphincter has been compared with the extent of sensation to light touch in the anal canal. At rest, the sphincteric zone was the longer. On distension of the rectum, a decrease in pressure in the anal canal so shortened the functional sphincter that intrarectal pressure extended down to contact the sensory zone. This mechanism may allow the sensation in the anal canal to play a part in the fine adjustment of anal continence.