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RYTHMIC EXCITATION OF THE HEART - Coggle Diagram
RYTHMIC EXCITATION OF THE HEART
Generation of Heart's Electrical Activity
Sinoatrial Node (SA Node)
Location: Right atrium
Function: Pacemaker of the heart (sets rhythm)
Spontaneous Depolarization: Due to slow Na+ influx and Ca2+ entry
Threshold reached → Initiates action potential (AP)
Spread of Action Potential
Atria: Action potential spreads through atrial muscle fibers (atrial contraction)
Atrioventricular Node (AV Node)
Location: Near the tricuspid valve in the right atrium
Delay: 0.1 second delay to allow for atrial contraction before ventricular filling
Bundle of His and Bundle Branches
AV Bundle (Bundle of His): Transmits action potential from AV node to ventricles
Right and Left Bundle Branches: Conduct the AP down the interventricular septum to each ventricle
Purkinje Fibers
Purkinje System: Spreads the action potential rapidly through the ventricular myocardium
Ventricular Contraction: Causes synchronized contraction of both ventricles
5) Action Potential Phases in
Cardiac Muscle Cells
Phase 0: Rapid depolarization (Na+ influx)
Phase 1: Initial repolarization (K+ efflux)
Phase 2: Plateau phase (Ca2+ influx, K+ efflux)
Phase 3: Final repolarization (K+ efflux)
Phase 4: Resting membrane potential
6) Refractory Period
Absolute Refractory Period: No new action potential can be initiated
Relative Refractory Period: A stronger stimulus can initiate an action potential
Important for preventing arrhythmias
7) Autonomic Control
Sympathetic Nervous System (SNS): Releases norepinephrine → Increases heart rate (positive chronotropic effect)
Parasympathetic Nervous System (PNS): Releases acetylcholine → Decreases heart rate (negative chronotropic effect)
8) Heart Rate Regulation
Normal Resting Rate: 60-100 beats per minute (bpm)
Influence of External Factors: Hormones (epinephrine), exercise, temperature, and emotions