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
Muscles have which efferent nerve fibers for regulating tone? 
Select and explain. 
A. a-neuron, B. Gamma neuron, C. Beta neuron, D. Delta neuron
B: Gamma neuron
Answer: B: Gamma neuron 
Explanation: 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).