Final answer:
All of the components of an ECG curve upward except the ST segment, which is a flat period between ventricular depolarization and repolarization.
Step-by-step explanation:
The question asks which component of the ECG does not curve upward. Looking at the standard components of an ECG, we can identify the following:
The P wave, which represents the depolarization of the atria.
The QRS complex, which represents the depolarization of the ventricles.
The T wave, which represents the repolarization of the ventricles.
ST segment, which is the period between ventricular depolarization and repolarization and usually does not curve upwards.
Given these components, all except the ST segment generally curve upward on an ECG.