Biological Systems MCAT Practice Exam

What is the role of the Purkinje fibers in the heart?

1. Generate electrical impulses

2. Distribute electrical impulses

3. Receive impulses from the SA node

4. Contract heart muscles

The correct answer is: Distribute electrical impulses

The Purkinje fibers play a crucial role in the conduction system of the heart by distributing electrical impulses throughout the ventricles. This distribution is essential for ensuring that the ventricles contract in a coordinated manner, allowing for effective pumping of blood to the lungs and the rest of the body. These specialized fibers conduct electrical signals rapidly and efficiently, leading to synchronous contraction of the ventricular muscle cells. This timing is vital to maximize the heart's effectiveness during the cardiac cycle. By facilitating the rapid spread of impulses initiated by the atrioventricular bundle (also known as the bundle of His), the Purkinje fibers ensure that the ventricles contract from the apex upwards towards the base of the heart, promoting effective blood ejection. The other roles mentioned in the choices are not functions of Purkinje fibers. For instance, the generation of electrical impulses is primarily the function of the sinoatrial node, which acts as the heart's natural pacemaker. Similarly, while the atrioventricular node receives impulses from the SA node, Purkinje fibers are not involved in receiving impulses, but rather in the distribution of those that have already been generated and processed through the conduction pathway. The contraction of heart muscles is a result of the impulses they distribute,