Question

Origin of heartbeat and its conduction is represented by
A. AV node →Bundle of His →SA node →Purkinje fibres
B. SA node →Purkinje fibres →AV node → Bundle of His
C. Purkinje fibres →AV node →SA node →Bundle of His
D. SA node →AV node → Bundle of His →Purkinje fibres

Answer 1

Hint: The impulse of heartbeat first originates in the SA node which has a cluster of cells and it is situated in the right chamber of heart. One heartbeat includes one cardiac cycle.

Complete answer:
First, the impulse for heart beat originated in the SA node which is also called the Sinus node. It is known as the heart's natural pacemaker. It has a cluster of cells which are situated in the upper right corner of the right atrium which is the right chamber of the heart.
This electrical impulse from the SA node is then conducted to the Atrioventricular Node or AV node which is a part of the electrical conduction system of the heart. It electrically connects atria and ventricles.
Now, the impulse gets transmitted from the AV node to the AV bundle which is known as the bundle of His. This bundle of His conducts the electrical impulses that regulate the heartbeat and it conveys the impulse of contractions to the apex of myocardium.
The impulses cause the Purkinje fibres to sweep upwards and outwards in order to pump the blood into the aorta and pulmonary artery.

Now, if we look at options, Option A is AV node →Bundle of His →SA node →Purkinje fibres. It is incorrect since impulse originates in the SA node but in this option the first step is AV node which is incorrect and thus it gets eliminated.
Moving to option B which is SA node →Purkinje fibres →AV node → Bundle of His. This option is also incorrect since the first step is fine as the impulse originates in the SA node but it is then conducted to AV node not purkinje fibres. Therefore, it is incorrect and it gets eliminated.
Moving to option C which is Purkinje fibres →AV node →SA node →Bundle of His. It is incorrect since impulse originates in the SA node but in this option the first step is purkinje fibres which is incorrect and thus it gets eliminated.
Last option D is SA node →AV node → Bundle of His →Purkinje fibres. It is the correct option. As explained above the impulse first originates in SA node and then it is conducted to AV node and then to the bundle of his and then to purkinje fibres. Therefore, it is the correct option.

Thus, the correct answer is option D.

Note: First the impulse is originated in the SA node and then it is conducted to the AV node. From the AV node it is transmitted to AV bundle which is also called a bundle of His, from the AV bundle the impulse causes the purkinje fibres to sweep upwards and outwards from the pumping of blood.