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
Dynamic response is due to 
Select and explain. 
A. Primary ending, B. Secondary ending, C. Tertiary ending, D. All
A: Primary ending
Answer: A: Primary ending 
Explanation: Nuclear bag fibers are thicker, longer and fewer in numbers. They have a bag or bulge in the centre where the afferent fibers received are Aα type with primary ending (Annulospiral). The efferent fibers are Aγ1, which are dynamic fibers with ‘plate ending’.
Nuclear chain fibers are thinner, shorter and more in numbers. They do not have a bulge, but receives afferent fibers of type Aα with primary ending (Annulospiral). The peripheral part also receives afferent fibers of type Aβ with secondary ending (Flower spray). The efferent fibers are Aγ2 static fibers with ‘trail ending’.