In Normal Sinus Rhythm (NSR),the

Question

In normal sinus rhythm (NSR),the
A) cardiac impulse originates in the sinoatrial node.
B) action potential originates in the AV node.
C) AV node activates the SA node.
D) action potential is generated by the sympathetic nerve.

Accepted Answer

In normal sinus rhythm (NSR), the cardiac impulse (or action potential) originates in the sinoatrial (SA) node, which serves as the heart's natural pacemaker. The SA node initiates and coordinates the electrical activity that causes the atria to contract and then sends the impulse to the atrioventricular (AV) node for further conduction to the ventricles. Option B is incorrect because the AV node serves as a delay and relay station, not the site of impulse initiation. Option C is incorrect because the SA node activates the AV node, not vice versa. Option D is incorrect because sympathetic nerve stimulation can modify heart rate but does not generate the cardiac impulse in NSR.