Intrinsic control of heartbeat rate involves what mechanism(s)?


a) The AV node initiates heartbeat although the SA node can generate a slower beat rate.

b) The atrioventricular bundle initiates signals that travel to the Purkinje fibers.

c) The SA node initiates heartbeat although the AV node can generate a slower beat rate.

d) The SA node initiates heartbeat and the AV node inhibits the heartbeat.

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To determine the correct answer, let's break down each option and explain the mechanism involved:

a) The AV (atrioventricular) node initiates the heartbeat, while the SA (sinoatrial) node can generate a slower beat rate. This mechanism is not part of the intrinsic control of heartbeat, as the AV node is responsible for conducting electrical signals between the atria and ventricles, but not initiating the heartbeat. Therefore, option a is incorrect.

b) The atrioventricular bundle (also known as the bundle of His) initiates electrical signals that travel to the Purkinje fibers, which then distribute the signals throughout the ventricles. This mechanism is part of the intrinsic control of heartbeat, as the atrioventricular bundle plays a vital role in synchronizing contraction of the ventricles. Thus, option b is a potential correct answer.

c) The SA node initiates the heartbeat, while the AV node can generate a slower beat rate. This option is not accurate because the SA node, located in the right atrium, is indeed responsible for initiating the heartbeat by generating electrical impulses. Additionally, the AV node, located between the atria and ventricles, functions to relay and delay the electrical signals rather than generating a slower beat rate. Therefore, option c is incorrect.

d) The SA node initiates the heartbeat, and the AV node inhibits the heartbeat. This option is also not accurate. While the SA node initiates the heartbeat as mentioned previously, the AV node does not inhibit the heartbeat. Instead, its role is to relay the electrical impulses from the atria to the ventricles. Therefore, option d is incorrect.

Based on the explanations above, option b (The atrioventricular bundle initiates signals that travel to the Purkinje fibers) is the correct answer for the mechanism involved in the intrinsic control of heartbeat.