Final answer:
The P wave on an electrocardiogram (ECG) represents the sinoatrial node impulse, wave of depolarization through the atria, and resultant contraction, indicating atrial depolarization.
Step-by-step explanation:
The small upward curve that represents the sinoatrial node impulse, wave of depolarization through the atria, and resultant contraction on an electrocardiogram (ECG) is known as the P wave.
The P wave signifies atrial depolarization, which is the electrical activity that initiates the contraction of the atria and precedes the pumping of blood into the ventricles.
Following the P wave comes the QRS complex, which indicates ventricular depolarization, and the T wave, which signifies ventricular repolarization.
It's important to note that the repolarization of the atria is masked by the QRS complex and is not visible on the ECG.