This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
All are true about cardiac muscle EXCEPT? 
Select and explain. 
A. Phase 1 of depolarization is due to opening of voltage gated sodium channels, B. Phase 2 of depolarization is due to slow opening of voltage gated calcium channels, C. Phase 3 of repolarization is due to K+ efflux, D. Tetany of cardiac muscle is never seen
A: Phase 1 of depolarization is due to opening of voltage gated sodium channels
Answer: A: Phase 1 of depolarization is due to opening of voltage gated sodium channels 
Explanation: Ans. A Phase 1 of depolarization is due to opening of voltage gated sodium channelsPhase 0 Rapid depolarization due to opening of voltage sensitive sodium channelsPhase 1 Rapid repolarization due to closure of sodium channels and opening of one type of K channelsPhase 2 Plateau phase due to slow and prolonged opening of voltage gated calcium channelsPhase 3 Final repolarization to RMP is due to closure of Ca++ and 4 channels and a slow delayed increase of K+ effluxSince cardiac muscle remains in refractory period until phase 4, tetanic contractions which can occur in skeletal muscle cannot occur in cardiac muscle.