Question

SAN is called the pacemaker because

1. It cannot generate an action potential to set the heart rate at 70-75 beats/min-1

2. It is responsible for initiating and maintaining the rhythmic contractile activity of heart

3. It is directly responsible for ventricular contraction which occurs with large force

4. It is made up of cardiac muscles​

Answer 1

Explanation:

The sinoatrial node (SAN) is called the natural pacemaker of the heart. This is because the SAN generates the maximum number of action potentials and is responsible for initiating and maintaining the rhythmic contractions of the heart.