Cardiac Action Potential and ECG Quiz

Heart Structure and Function

• The myocardium consists of the main muscle layer of the heart.
• The coronary arteries are located in the epicardium, the outermost layer of the heart's walls.
• The obtuse marginal branch of the left circumflex coronary artery supplies the lateral wall of the left ventricle.

Blood Flow and Oxygen Demand

• During physical stress, blood flow in coronary vessels increases to meet the increased oxygen demand.
• If the coronary artery is occluded by more than 70%, resting blood flow becomes insufficient to meet oxygen demand.
• The heart plays a crucial role in supplying blood to the body, and any disruption in blood flow can lead to tissue hypoxia.

Tissue Hypoxia and Coronary Occlusion

• The primary cause of tissue hypoxia in the myocardium during activities like running is the inability of the coronary circulation to meet the increased oxygen demand.
• Atherosclerosis, a process of plaque buildup, may result in complete occlusion of the vessel supplying a specific region of the myocardium.

Action Potentials in Cardiac Cells

• The main characteristic of Phase 0 of the fast-response action potential in cardiac cells is a rapid depolarization due to the influx of sodium ions.
• Fast-response action potentials occur in atrial and ventricular myocardial fibers as well as Purkinje fibers.
• The plateau phase in the fast-response action potential is primarily maintained by the influx of calcium ions.
• The release of a large amount of calcium into the cytosol from the sarcoplasmic reticulum during myocardial contraction is triggered by the depolarization of the sarcolemma.
• Ventricular contraction is sustained throughout the action potential during Phase 2.
• Potassium ions are mainly responsible for repolarization during Phase 3 of the fast-response action potential.
• 'Restoration of ionic concentrations' during Phase 4 is primarily mediated by the Na+/K+ ATPase pump.
• The 'ATP-driven Ca++ Pump' is responsible for the reuptake of calcium ions into the sarcoplasmic reticulum during Phase 4.