This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Muscles have which efferent nerve fibers for regulating tone? \nSelect and explain. \nA. a-neuron, B. Gamma neuron, C. Beta neuron, D. Delta neuron', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Gamma neuron(Ref: Ganong 23'd/e p.158-162; Guyton 12n/e p. 657)Muscle tone is maintained by stretch reflex through muscle spindles (intrafusal fibers).", 'role': 'assistant'}]