Final answer:
The defecation reflex involves mass movements in the colon and a series of muscular contractions and relaxations, which can be temporarily suppressed by applying pressure to the anus to delay the urge to defecate.
Step-by-step explanation:
The question pertains to the control of the defecation reflex, which involves a series of events to eliminate feces from the rectum. Mass movements in the colon force feces into the rectum, triggering the defecation reflex. This reflex is mediated by the spinal cord and involves the contraction of the sigmoid colon and rectum, relaxation of the internal anaI sphincter, and the initial contraction of the external anaI sphincter. Should an individual choose to delay defecation, applying pressure and covering the anus can temporarily suppress this urge by allowing time for the reflex contractions to cease and the rectal walls to relax. Subsequent mass movements will prompt the reflex again until eventual defecation occurs.