This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conducting System of Hea, Subject name: Physiology
"Gate" cells in the hea are: 
Select and explain. 
A. Cells in SA node, B. Cells in AV node, C. Cells in his bundle, D. Cells in Purkinje fibers
D: Cells in Purkinje fibers
Answer: D: Cells in Purkinje fibers 
Explanation: Purkinje fibers at the apex, where impulse is passed on from Purkinje fibers to ventricular muscle, are the so-called "gate cells".