Determine whether each statement correctly describes the myocardial action potential and the pacemaker potential. 1. Because the pacemaker potential occurs during systole, it can also be called systolic potential. (Click to select) 2. The pacemaker potential is the relatively slow, spontaneous depolarization in the SA node. (Click to select) 3. Myocardial cells produce their own action potentials after being stimulated by action potentials originating in the SA node. (Click to select) 4. Myocardial action potentials are characterized by a spike and then slow depolarization. (Click to select)

1. False

2. True

3. True

4. False

Explanation:

In mammals, the contraction of the heart muscle is caused by pacemaker cells localized within the sinoatrial (SA) node. These cells rhythmically generate slow electrically-induced action potentials due to their slow rate of depolarization. The pacemaker cells generate the action potentials that propagate through the heart and trigger the contraction of myocyte cells (i.e., myocytes simply conduct the action potential waves). The slow depolarization of pacemaker cells occurs during diastole, i.e., during the period of relaxation of the heart muscle.

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