The P wave of the electrocardiogram is a signal from
depolarization of the ventricles.
the SA node.
depolarization of the AV node.
repolarization of the atria.
depolarization of the atria
The correct answer and explanation is :
The correct answer is: depolarization of the atria.
Explanation:
The electrocardiogram (ECG) is a graphical representation of the electrical activity of the heart. It shows the timing and duration of electrical impulses that cause the heart to contract. The P wave on an ECG specifically represents the depolarization of the atria.
- Depolarization of the Atria: The heart’s electrical impulses originate in the sinoatrial (SA) node, a small cluster of cells located in the right atrium. When the SA node fires, the electrical impulse spreads through the atria, causing them to contract and push blood into the ventricles. The electrical activity of this contraction is captured as the P wave on the ECG. It represents the depolarization process, where the atrial cells become electrically excited and prepare for contraction.
- Why Not Other Options?
- Depolarization of the Ventricles: The QRS complex on the ECG represents the depolarization of the ventricles, not the P wave. This is a larger electrical impulse since the ventricles are much more muscular and have greater electrical activity compared to the atria.
- The SA Node: The SA node itself is responsible for initiating the electrical impulse but is not directly reflected by the P wave. It sends an electrical signal to the atria, which is what is captured as the P wave on the ECG.
- Depolarization of the AV Node: The AV node is part of the conduction system of the heart, located between the atria and ventricles. The electrical impulse is briefly delayed at the AV node to allow the ventricles time to fill before contraction. This delay is not represented by the P wave, but instead is part of the PR interval on the ECG.
- Repolarization of the Atria: The T wave represents the repolarization of the ventricles. Atrial repolarization occurs at the same time as the QRS complex but is not visually represented due to the larger ventricular depolarization signal.
Thus, the P wave specifically represents the depolarization of the atria, which is the first phase in the heart’s electrical cycle.