A: The resting heart rate,about 75 beats/minu | vedclass

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(A) The $SA$ node (Sinoatrial node) acts as the natural pacemaker of the heart,with an intrinsic autorhythmic rate of approximately $90-100$ beats per

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Assertion and Reason both are correct and Reason is the correct explanation of Assertion.

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(A) The $SA$ node (Sinoatrial node) acts as the natural pacemaker of the heart,with an intrinsic autorhythmic rate of approximately $90-100$ beats per minute.However,the resting heart rate in a healthy adult is typically around $70-75$ beats per minute.This difference occurs because the autonomic nervous system modulates the heart rate.At rest,the parasympathetic nervous system (via the vagus nerve) releases acetylcholine,which slows down the firing rate of the $SA$ node,thereby decreasing the heart rate.Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

$A$: The resting heart rate,about $75$ beats/minute,is usually lower than the autorhythmic rate of the $SA$ node ($90-100$ beats/minute).
$R$: At rest,the parasympathetic nervous system effects dominate the heart rate.

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$A$: The resting heart rate,about $75$ beats/minute,is usually lower than the autorhythmic rate of the $SA$ node ($90-100$ beats/minute).$R$: At rest,the parasympathetic nervous system effects dominate the heart rate.