Assertion A: Cardiac excitation normally begins in the sinoatrial (SA) node.
Reason R: SA node cells do not have a stable resting potential. They depolarize to threshold spontaneously.
In the light of the above statements, choose the most appropriate answer from the options given below
Cardiac Excitation Analysis: SA Node Function
This question asks us to evaluate two statements regarding the origin of cardiac excitation and the properties of the SA node.
Assertion A Analysis
Assertion A states that cardiac excitation normally begins in the sinoatrial (SA) node. This is a fundamental concept in cardiovascular physiology. The SA node, located in the upper wall of the right atrium, acts as the heart's natural pacemaker. It initiates the electrical impulse that triggers atrial contraction and subsequently leads to ventricular contraction, thus controlling the heart rate.
- Assertion A is correct.
Reason R Analysis
Reason R states that SA node cells do not have a stable resting potential and depolarize to threshold spontaneously. This property is known as automaticity. Unlike typical cardiac muscle cells or neurons that maintain a stable negative resting membrane potential, SA node cells exhibit a "pacemaker potential." Their membrane potential gradually drifts towards the threshold potential without external stimulation, causing them to fire action potentials rhythmically.
- Reason R is correct.
Relationship Between Assertion A and Reason R
The spontaneous depolarization (automaticity) described in Reason R is precisely the mechanism that allows the SA node to act as the primary pacemaker and initiate cardiac excitation, as stated in Assertion A. Because the SA node cells can generate impulses spontaneously and rhythmically, they set the pace for the entire heart.
- Therefore, Reason R provides the correct physiological explanation for why Assertion A is true.
Conclusion
Both statements are factually correct, and Reason R accurately explains Assertion A.
The most appropriate answer is: Both A and R are correct and R is the correct explanation of A.
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Important Questions from Mixed Topic (CUET PG)
- Kalpsutra, the illustrated canonical text is from:-
- The Harappan city almost exclusively devoted to craft production was-:
- Mohandas Karamchand Gandhi launched quit India movement after the failure of:-
- The "Objectives Resolution" was introduced in constituent assembly by:-
- Who among the following was not a member of the constituent assembly:-
