<P> Depolarization occurs in the four chambers of the heart: both atria first, and then both ventricles . </P> <Ol> <Li> The sinoatrial (SA) node on the wall of the right atrium initiates depolarization in the right and left atria, causing contraction, which is symbolized by the P wave on an electrocardiogram . </Li> <Li> The SA node sends the depolarization wave to the atrioventricular (AV) node which--with about a 100 ms delay to let the atria finish contracting--then causes contraction in both ventricles, seen in the QRS wave . At the same time, the atria re-polarize and relax . </Li> <Li> The ventricles are re-polarized and relaxed at the T wave . </Li> </Ol> <Li> The sinoatrial (SA) node on the wall of the right atrium initiates depolarization in the right and left atria, causing contraction, which is symbolized by the P wave on an electrocardiogram . </Li> <Li> The SA node sends the depolarization wave to the atrioventricular (AV) node which--with about a 100 ms delay to let the atria finish contracting--then causes contraction in both ventricles, seen in the QRS wave . At the same time, the atria re-polarize and relax . </Li>

What is the purpose of the transmembrane potential across the neurilemma