A. Gap Junctions
Explanation - Cardiac muscle cell are able to contract in synchronized manner because of the gap junctions of intercalated discs. The action potential is expanded by the gap junction to support the coordinated contraction of the cardiac muscle.
Excitation contraction coupling or ECC is the process by which contraction of muscle occurs. It converts the electrical stimulus sent by the neurons to mechanical response to promote the movement of the muscle. Gap junctions thus helps in connecting the cardiac muscle cell.