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Respiration and Circulation — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYRespiration and Circulation4 Marks
Question
What is repolarization and depolarization ?
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Answer

Repolarization is a stage of an action potential in which the cell experiences a reduction of voltage due to the efflux of potassium $(K^+)$ ions along its electrochemical gradient. This phase occurs after the cell reaches its highest voltage from depolarization.
Depolarization occurs in the four chambers of the heart : both atria first and then both ventricles. The $SA$ node sends the depolarization wave to the atrioventricular $(AV)$ node which$-$with about a $100$ minutes delay to let the atria finish contracting$-$then causes contraction in both ventricles, seen in the $\text{QRS}$ wave.

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