What physiological change occurs during the P wave on an electrocardiogram?

The P wave on an electrocardiogram (ECG) represents atrial depolarization. This is the process in which the electrical signals spread through the atria, stimulating them to contract and push blood into the ventricles. Depolarization refers to the change in electrical charge across the cell membranes of the atrial muscle cells, which is essential for initiating the contraction of the atria.

Understanding this physiological event is crucial for interpreting ECGs and the overall electrical activity of the heart. The P wave is a crucial part of the cardiac cycle, as it precedes the atrial contraction, allowing efficient filling of the ventricles. This process plays an important role in maintaining coordinated timing and synchronization in the heart's pumping action.

In contrast, other options relate to different phases of the cardiac cycle: ventricular contraction occurs later and is represented by the QRS complex, while atrial repolarization occurs during the QRS complex and is not prominently visible on the ECG. Therefore, the signature feature of the P wave is its representation of atrial depolarization.