MICROANATOMY

Detailed explanation-1: -The cardiac action potential originates in specialized cells at the right atrium called the sinoatrial (SA) node, the natural pacemaker of the heart. The cells in the SA node are enriched in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

Detailed explanation-2: -The heart’s intrinsic pacemaker, the sinoatrial node (SAN), generates spontaneous action potentials (AP) through a system of coupled oscillators whose common output initiates each normal heartbeat.

Detailed explanation-3: -The fast sodium channel These sodium channels are voltage-dependent, opening rapidly due to depolarization of the membrane, which usually occurs from neighboring cells, through gap junctions. They allow for a rapid flow of sodium into the cell, depolarizing the membrane completely and initiating an action potential.