Control of the Cardiac Cycle

Sinoatrial Node (SAN) - The hearts natural pacemaker. A small patch of tissue that sends out a wave of electrical excitation at regular intervals to initiate contractions. 

Purkyne Tissue - Specially adapted muscle fibers that conduct the wave of excitation from the AVN down the septum to the ventricles. 

Coordinating the heart beat

- SAN initiates a wave of excitation. 

- The excitation wave spreads over the walls of the atria. 

- At the base of the atria is a dic of tissue that cannot conduct the excitation wave. 

- The excitation wave is delayed in the AVN (between the atria and ventricles). The delay allows time for the atria to finish contracting and so the ventricles don't contract too soon (the…