1.The thought or smell of food, distention of the stomach, and the movement of chyme into the duodenum can stimulate the gastrocolic and duodenocolic reflexes( green arrows)
2.The gastrocolic and duodenocolic reflexes stimulate mass movement in the colon, which propel the contents of the colon toward the rectum (orange arrow)
3.Distention of the rectum by faces stimulates local defecation reflexes These reflexes cause contractions of the colon and rectum (brown arrow) , which move faces toward the anus
4.Local reflexes cause relaxation of the internal anal sphincter (brow arrow)
5.Distention of the rectum by faces stimulates parasympathetic reflexes. Action potentials are propagated to the defecation reflex center located in the defecation reflex center located in the spinal cord (yellow arrow)
6.Action potentials stimulate contraction of the colon and rectum and relaxation of the internal anal sphincter( purple arrow)
7.Action potentials propagated through ascending nerve tracts to the brain (blue arrow)
8.Descending nerve tracts from the brain regulate the defecation reflex center ( pink arrow)
9.Action potentials form the brain control the external anal sphincter( purple arrow)