So let's recall where the heart actually begins, where it generates that electrical signal. So within the right atrium, within the upper wall of the right atrium, we have a collection of specialized cells that collectively are called the sinoatrial node, or simply the SA node. So this is where the SA node is located. And the essay note contains cells where the membrane of those cells depolarize. And that creates an electrical potential difference. And that's exactly why we have an increase in the voltage taking place within this portion.