Parasympathetic Defecation Reflex
The parasympathetic defecation reflex works in essentially the same way as the intrinsic myenteric defecation reflex but involves parasympathetic nerve fibers in the pelvic nerves. It triggers peristaltic waves in the descending and sigmoid colon as well as the rectum. It also causes relaxation of the external anal sphincter. The difference is that the parasympathetic defecation reflex enhances this process and makes the intrinsic reflex much more powerful. If sufficiently stimulated, it may even cause the sigmoid colon to completely empty all of its contents in the rectum rapidly.