Final answer:
An ECG reflects the heart's electrical activity, with the P wave indicating atrial depolarization, the QRS complex representing ventricular depolarization, and the T wave signifying ventricular repolarization.
Step-by-step explanation:
The ECG (electrocardiogram) is crucial for understanding the electrical activity of the heart and comprises various waves and complexes that represent heart muscle depolarization and repolarization. Notably, there is the P wave, the QRS complex, and the T wave.
The P wave indicates the depolarization of the atria, which is the initial electrical change associated with the atria contracting and pumping blood into the ventricles. Following the P wave, atrial contraction occurs approximately 25 milliseconds later.
The QRS complex, particularly significant due to its larger amplitude, signifies ventricular depolarization. This is a process requiring a more intense electrical signal because the ventricles are larger muscle masses than the atria. The ventricles begin contracting around the peak of the R wave within the QRS complex. An important detail is that the repolarization of the atria, which happens concurrently with the QRS complex, is not visible on the ECG as it is masked by the larger signal of ventricular depolarization.
Finally, the T wave represents the repolarization of the ventricles, setting the stage for the heart muscle to relax in preparation for the next cardiac cycle.