Defecation depends on

a. distention of the rectal wall

b. sensory impulses to the sacral spinal cord

c. motor impulses back to the colon

d. all of the above must happen for defecation to occur

Answer: the correct answer is d. all of the above must happen for defecation to occur.

Explanation:

In response to the distention of the rectal wall, the receptors send sensory nerve impulses to the sacral spinal cord. Motor impulses from the cord travel along parasympathetic nerves back to the descending colon, sigmoid colon, rectum, and anus. The resulting contraction of the longitudinal rectal muscles shortens the rectum, thereby increasing the pressure within it. This then opens the internal sphincter.