Answer:
The correct answer is: Electrical impulses in the heart cause the muscles to contract.
Explanation:
The heart contracts thanks to a series of electrical impulses that travel through the muscles of this organ. The electrical impulse begins in the SA (sinoatrial) node and is transmitted to the muscles that conform the left and the right atria to produce their contraction which will make the atria pump the blood to the ventricles. When the electrical impulse reaches the AV node and then the Bundle of His, this information will transmit to both ventricles and will produce their contraction as well.
The only muscle tissue capable of stimulating their own contractions is the muscle in the heart, the myocardium, thanks to the existence of "pacemaker cells" that are located in the SA node.
The waves in the ECG represent the depolarization of the atria, depolarization of the ventricles, and repolarization of the ventricles.
