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: Surgery
Gate control theory of pain is due to 
Select and explain. 
A. Substantial gelatinosa, B. A delta fibres, C. C-fibres, D. Free nerve endings
A: Substantial gelatinosa
Answer: A: Substantial gelatinosa 
Explanation: None