ANATOMY

Detailed explanation-1: -This gradual depolarization mainly occurs via a depolarization current or pacemaker current (If). Pacemaker current occurs due to the slow influx of Na+ ions through the hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel).

Detailed explanation-2: -Cells within the sinus node have the fastest rate of spontaneous depolarization, and, therefore, the sinus node is the main pacemaker region of the heart. The AV node has the second fastest rate of spontaneous depolarization, which allows it to create an escape rhythm if the sinus node is diseased.

Detailed explanation-3: -Repolarization in the ventricles of the heart is a process allowing the muscle cells of the ventricles to regain their ability to depolarize again. Repolarization entails movement of the ions, which entered the cell during the depolarization phase of the cycle, to flow out of the cell.

Detailed explanation-4: -Which of the following occurs during depolarization of a cardiac cell? The cell becomes relatively more positively charged.