Which of the following statements about colonic motility is/are true?

A. Mass contractions involve only the rectum.

D. Stool in the colon is propelled by tonic contractions. 

E. Defecation involves both sensory and motor pathways.

DISCUSSION: Various patterns of motility are present in the colon. In the ascending colon “antiperistalsis” waves generate retrograde flow of colonic contents back to the cecum. In the descending colon contents are propelled caudad by tonic contractions, separating them into a series of globular masses. A third type of contraction, called mass peristalsis, occurs at varying intervals through the entire colon's length. Finally, the rectum will undergo receptive relaxation to accommodate stool until defecation takes place. Normal defecation involves the perception and discrimination of stool and gas in the rectum, deferment of stool elimination until a socially acceptable time, expulsion of stool, and sealing of the anal canal. These processes depend on various sensory and motor pathways.