Question

the opening of the internal sphincters is through action of the _______ .
a somatic nervous system
b enteric nervous system
c sympathetic nervous system
d parasympathetic nervous system

Explanation:

To solve this, we analyze each option:

• Option A: The somatic nervous system controls voluntary movements (e.g., skeletal muscle), not internal sphincters' opening. Eliminate A.
• Option B: The enteric nervous system (ENS) regulates the gastrointestinal tract, including sphincter function. But let's check others.
• Option C: The sympathetic nervous system generally inhibits digestive functions (e.g., slows gut motility), so it doesn't open internal sphincters. Eliminate C.
• Option D: The parasympathetic nervous system promotes "rest - and - digest" functions, including opening internal sphincters for processes like defecation/urination. However, the enteric nervous system (B) is part of the autonomic nervous system and directly controls gut - related sphincters. Wait, correction: Internal sphincters (e.g., in the anus, urethra) are controlled by the enteric nervous system? No, actually, the enteric nervous system is a division of the autonomic nervous system that controls the gastrointestinal tract. But for internal sphincters (like the internal anal sphincter), the enteric nervous system (ENS) is the primary controller. Wait, no, let's recall: The internal anal sphincter is smooth muscle, controlled by the enteric nervous system (part of the autonomic). The parasympathetic also influences, but the enteric nervous system is more direct for gut - associated sphincters. Wait, maybe I made a mistake earlier. Let's re - evaluate:

The enteric nervous system (ENS) is a complex network of neurons in the gut wall that controls gastrointestinal motility, secretion, and blood flow, including sphincter function. The somatic nervous system (A) is voluntary, so not for internal (involuntary) sphincters. Sympathetic (C) is "fight - or - flight", which would tend to close or inhibit opening of internal sphincters. Parasympathetic (D) is "rest - and - digest", but for gut - related internal sphincters, the enteric nervous system (B) is the key. Wait, no, actually, the internal sphincters (like the internal urethral sphincter) are controlled by the sympathetic and parasympathetic, but for the internal anal sphincter, it's the enteric. Wait, the question is about "internal sphincters" in general. The enteric nervous system is responsible for the function of the gastrointestinal sphincters. So the correct answer is B.

Answer:

B. enteric nervous system