Distention of the rectal wall by faces stimulates the defecation reflex, which consists of local and parasympathetic reflexes cause strong contractions and are normally responsible for most of the defecation reflex. Local reflexes cause weak contractions of the distal colon and rectum and relaxation of the internal anal sphincter (figure 21.25, steps 3 and 4) Defecation requires that the contractions that move feces toward the anus be coordinated with the relaxation of the internal and external anal sphincters.