Question

Defaecation is a reflex action 

A. That is coordinated by reflex centres in the sacral cord. 

B. Whose afferent limb carries impulses from stretch receptors in the colon. 

C. Whose efferent limb travels mainly in sympathetic autonomic nerves. 

D. Which is more likely to be initiated just after a meal than just before it. 

E. Which can be voluntarily inhibited or facilitated.

Answer 1

A. True Reflex defaecation can occur after complete spinal cord transection. 

B. False The stretch receptors triggering the reflex are in the rectal wall. 

C. False Parasympathetic nerves are the main motor nerves for defaecation. 

D. True The wish to defaecate that follows a meal is attributed to a ‘gastrocolic reflex’. 

E. True Forced expiration against a closed glottis facilitates the reflex by raising intraabdominal pressure and pushing faeces into the rectum; contraction of the voluntary muscle of the external sphincter can inhibit it.