A: The cardiac impulse which originates from | vedclass

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(A) The $SA$ node (Sinoatrial node) acts as the pacemaker of the heart,initiating the electrical impulse.This impulse spreads through the atria,causin

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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 pacemaker of the heart,initiating the electrical impulse.This impulse spreads through the atria,causing atrial contraction.However,there is a fibrous connective tissue layer (the fibrous skeleton of the heart) that acts as an electrical insulator between the atria and the ventricles.Because of this,the impulse cannot spread directly from the atrial muscle to the ventricular muscle.The only electrical connection between the atria and the ventricles is the $AV$ bundle (Bundle of His),which conducts the impulse to the ventricles.Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why the impulse cannot spread directly.

$A$: The cardiac impulse which originates from $SA$ node in mammalian heart cannot spread directly from atria to ventricles.
$R$: In mammalian heart there is no continuity between cardiac muscle fibres of atria and those of ventricles except $AV$ bundles.

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$A$: The cardiac impulse which originates from $SA$ node in mammalian heart cannot spread directly from atria to ventricles.$R$: In mammalian heart there is no continuity between cardiac muscle fibres of atria and those of ventricles except $AV$ bundles.