<span>The SA nodes sends out electrical impulses that regulates the heartbeat. The SA also called the sinus node generates the electrical signals which moves from cell to cell down through the heart until it reaches the atrioventricular node, a cluster of cells situated in the center of the heart between the atria and ventricles. In other words, SA nodes controls the heart rate by generating electrical impulses and then sending signals through the heart muscle, causing the heart to contract and pump blood throughout the body. </span>
The SA node<span> is the heart's natural pacemaker consisting of a cluster of cells located in the upper part of the wall of the right atrium. (the right upper chamber of the heart). The electrical impulses are produced and sent out from there to regulate heartbeat. This is also called the sinus code. </span>
The answer is number two extinction happened, this was the time dinosaurs went extinct ebcause lack of sun because oh how much dirt was blown into the earth atmosphere becuase of the asteriod, third option is talking about big bang theroy so that dosnt apply!
