Question

Rate of heart beat is determined by

• A. Purkinje fibres
• B. papillary muscles
• C. AV-node
• D. SA-node.

Answer 1

The Correct Option is D

The rate of the heartbeat is determined by the Sinoatrial Node (SA node), which is known as the natural pacemaker of the heart. To understand why the SA node is responsible for this, let's break down the cardiac conduction system:

1. SA Node: Located in the right atrium, the SA node generates electrical impulses that initiate the heartbeat. It sets the rhythm and rate by sending signals to the atria, causing them to contract and push blood into the ventricles.
2. AV Node: The Atrioventricular Node receives impulses from the SA node and acts as a gateway to the ventricles. It helps delay the signal slightly, ensuring the atria empty blood into the ventricles before they contract. While important, it does not determine the heartbeat rate but only passes along the signals set by the SA node.
3. Purkinje Fibres: These fibers rapidly conduct the impulse to the ventricles, ensuring they contract simultaneously and effectively to push blood out of the heart. They play a role in contraction but not in setting the heart rate.
4. Papillary Muscles: These muscles anchor the heart valves and help prevent them from inverting during ventricular contraction. They do not influence the heart rate.

Thus, the SA node is responsible for determining the rate of the heartbeat because it is the primary pacemaker of the heart.

The correct answer is therefore: SA-node.