The heartbeat is initiated and coordinated internally within the heart itself
The heart can beat independently without external signals
Sinoatrial node (SAN) or pacemaker
Located within the right atrium
Group of specialized cells
Depolarize, triggering an electrical excitation that spreads across the atria, causing them to contract (atrial systole)
The electrical excitation cannot pass directly to the ventricles due to a non-conducting layer of tissue separating them from the atria
Atrioventricular node (AVN)
Group of specialized cells between the atria
Connected to conducting fibers called Purkinje fibers
Detects the electrical excitation from the atria and, after a short delay, transmits it down the Purkinje fibers, causing the ventricles to contract from the apex upwards
The delay ensures that the ventricles contract after the atria, optimizing blood flow
