Cardiac Conduction System Describes the electrical events of the heart Autorhythmicity: electrical impulses generate within the heart, not from the nervous system SA node Pacemaker AV node AV bundle Purkinje fibers

Cardiac Cycle Describes the mechanical events of the heart Syncytium: a group of cells functioning as a single unit in sync Systole: contraction Diastole: relaxation

Atrial systole Beginning of cardiac cycle Caused by depolarization of SA node Forces blood from atria through AV valves into ventricles

Ventricular systole Caused by depolarization of Purkinje fibers AV valves are forced shut Forces blood from ventricles through semilunar valves into arteries Atria are in diastole

Ventricular diastole Blood passively fills atria Pressure in the atria builds until AV valves open and blood passively fills ventricle Semilunar valves close

The EKG