Anatomy and Physiology II Practice Test

What happens during ventricular depolarization?

1. The heart is in diastole

2. The ventricles contract

3. The atria contract

4. The heart rate decreases

The correct answer is: The ventricles contract

Ventricular depolarization is a critical phase in the cardiac cycle that corresponds to the electrical activation of the ventricles, leading to their contraction. During this process, the ventricles, which are the lower chambers of the heart, receive an electrical impulse that travels through the specialized conducting system, primarily the bundle of His and the Purkinje fibers. This causes the muscle fibers in the ventricles to contract forcefully, propelling blood out of the heart and into the arteries—the aorta and the pulmonary artery. This immediate transition from depolarization to contraction is important for maintaining effective circulation. As the ventricles contract, they pump oxygenated blood to the body and deoxygenated blood to the lungs for reoxygenation. The sequence of electrical activity followed by mechanical contraction exemplifies the heart's efficient electrical conduction system. In contrast, during diastole, the heart is in a state of relaxation, and there is no contraction happening in the ventricles. Atrial contraction occurs prior to ventricular depolarization and is part of the overall cardiac cycle, but it does not directly relate to ventricular depolarization itself. The heart rate may change due to various physiological factors, but it is not a direct result of ventricular depolarization.