What is the role of the external anal sphincter? What is the role of the external anal sphincter? Solution Answer: The external anal sphincter is skeletal muscle that can be consciously controlled, and is innervated by somatic efferent neurons. The external anal sphincter control evacuation of feces from the anus. If sufficient volume of feaces is deposited in the rectum, the increased pressure will stimulate a reflexive contraction in the sigmoid colon and rectum. Then it helps in defecation by its contraction..