Anatomical reminder about anal sphincter

This muscular set is located in the anal channel, between the anus and the rectum. This muscular system is dedicated to ensure the continence of the subject. We can decompose it in two part (see fig.1).

• The internal anal sphincter is composed by smooth muscular fiber and provided with a reflex type comportment.
• The external anal shincter is composed by ridge muscular fiber and is moved by a volunter action.

This two muscle are characterized by a permanent tonicity who just relaxed at defecation.

  
Figure 1: Schematic description of the anal sphincter