This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
In the hea, which muscarinic receptor inhibits adenyl cyclase activity? 
Select and explain. 
A. M1, B. M2, C. M3, D. M4
B: M2
Answer: B: M2 
Explanation: M2 receptors are located in the hea.Ref: HL Sharma 3rd ed Pg: 119