Why is the SA node the pacemaker of the heart? What is activates the SA node?

1. A. Why is the SA node the pacemaker of the heart? What is activates the SA node? B. How does the conducting system result in the contraction of the non-pacemaker myocytes of the atria and ventricles? (Include the parts of the system in your answer)

2. What is occurring in the 5 periods of the cardiac cycle? State weather the AV and semilunar valves are open or closed during each period and tell me which phase of the ECG is occurring during each period.

3. A. What is Mean Arterial Pressure and how is it measured? B. MAP is regulated by Cardiac Output. What components make up Cardiac Output? C. Tell me a factor that can increase stroke volume and what that change will do to the Mean Atrial Pressure? D. Differentiate the preload from the afterload and explain how each can increase and decrease Cardiac Output and thus MAP.