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: Physiology
Impulse is generated at fastest rate in 
Select and explain. 
A. AV node, B. SA node, C. Bundle of His, D. Purkinje fibers
B: SA node
Answer: B: SA node 
Explanation: Some cardiac fibers have the capability of self-excitation, a process that can cause automatic rhythmical discharge and contraction. This capability is especially true of the fibers of the hea's specialized conducting system, including the fibers of the sinus node. For this reason, the sinus node ordinarily controls the rate of beat of the entire heaRef: Guyton and Hall textbook of medical physiology 13th edition. Page:123