For both defecation and urination, the internal sphincters allowing exit of feces or urine are under involuntary control, while the external sphincters are under voluntary control (e.g. you choose when to open them).

What type of muscle are the internal and external sphincters made of and what part of the nervous system controls them to explain why one set is involuntary and the other voluntary? [Use the options in brackets as possible answer choices.]

A. Internal sphincter muscle type [skeletal, smooth, or cardiac]

B. Internal sphincter nervous system [somatic, sympathetic, parasympathetic]

C. External sphincter muscle type [skeletal, smooth, or cardiac]

D. External sphincter nervous system [somatic, sympathetic, parasympathetic]