What are the SA node and AV node?

The Sinoatrial (SA) node and the Atrioventricular (AV) node are both extremely important in the conduction events of the heart. The Sinoatrial node displays pacemaker activity - that is, it spontaneously depolarizes, setting in forth the chain of events that is required for contraction of the heart. Depolarization refers to the event in which positive ions flow into the heart, resulting in a voltage change in the heart, leading to contraction. From the SA node, the voltage is conducted through the internodal pathway to the AV node, in which the impulse is temporarily paused before been transmitted through the Bundle of His and the Left and Right bundle branches. These events, as previously mentioned, are extremely important in conduction pathways of the heart, and hence, the function of the heart :)