Question

what is depolarization and repolarization of the atria and ventricles. what is there significance?

Answer 1

Depolarisation of atria means contraction of both the atria simultaneously. It is caused by the activation of SA node. In ECG, P wave is produced due to atrial depolarization of atria.
Ventricular depolarization means contraction of both the ventricles simultaneously. It is caused by the impulses of the contraction from AV node through the bundle of His and Purkinje fibers and the contraction of the ventricular muscles. It produces QRS wave in ECG.
Ventricular repolarization means relaxation of both the ventricles simultaneously. It produces T wave in ECG.