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
Hot water bottle relieves the pain of abdominal spasm by 
Select and explain. 
A. Stimulation of adrenergic fibers, B. Stimulation of cholinergic fibers, C. Inhibition of cold receptors, D. Inhibition of heat receptors
A: Stimulation of adrenergic fibers
Answer: A: Stimulation of adrenergic fibers 
Explanation: Pain from gastrointestinal viscera is carried by small C fibers. Temperature sensation from hot water bottles passes through A fibers and large C fibers. 
When these larger fibers are stimulated, they block the adrenergic small C fibers from the viscera.