The normal pacemaker of the heart is the:
A.
Purkinje fibers.
B.
AV bundle.
C.
Sinoatrial node.
D.
Atrioventricular node.
The Correct Answer and Explanation is:
The correct answer is C. Sinoatrial node.
Explanation:
The heart’s normal pacemaker is the sinoatrial (SA) node. This specialized cluster of cells, located in the right atrium near the opening of the superior vena cava, is crucial for initiating the electrical impulses that regulate the heartbeat.
Function of the SA Node:
- Initiation of Heartbeat: The SA node generates electrical impulses spontaneously at a regular rate. These impulses are responsible for initiating the heartbeat and determining the heart rate. Under normal conditions, the SA node fires approximately 60 to 100 times per minute, setting the pace for the rest of the heart.
- Propagation of Impulses: The electrical impulses generated by the SA node travel through the atria, causing atrial contraction. This process helps to move blood from the atria into the ventricles. The impulse then reaches the atrioventricular (AV) node.
- Coordination of Heartbeat: The impulse from the SA node ensures that the atria contract first, followed by the ventricles. This coordination allows efficient blood flow through the heart and into the circulation.
Comparison with Other Nodes and Fibers:
- Purkinje Fibers (A): These fibers are part of the conduction system of the heart but are not responsible for initiating the heartbeat. They conduct impulses to the ventricular myocardium, facilitating synchronized ventricular contraction.
- AV Bundle (B): Also known as the Bundle of His, this structure carries the electrical impulse from the AV node to the Purkinje fibers. It is crucial for transmitting impulses to the ventricles but does not initiate the heartbeat.
- AV Node (D): The atrioventricular node is responsible for delaying the electrical impulse from the atria before it passes to the ventricles. This delay allows the ventricles to fill with blood from the atria before they contract. Although important in the conduction pathway, it does not act as the primary pacemaker.
In summary, the SA node is the heart’s natural pacemaker, setting the rhythm and coordinating the heartbeat through its spontaneous electrical impulses.
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