The Cardiomyocyte Action Potential [Part 1]: The Action Potential Graph

The video explains the action potential in heart muscle cells, focusing on the phases of depolarization, plateau, and repolarization. It distinguishes between pacemaker potentials and cardiomyocyte action potentials, emphasizing the role of sodium, potassium, and calcium channels. The plateau phase is crucial for effective blood ejection from heart chambers. The video also clarifies that the action potential is a cellular event, distinct from an electrocardiogram, and occurs in all heart cells during a cardiac cycle.

What is the primary difference between action potential and pacemaker potential in cardiomyocytes?

• Pacemaker potential initiates muscle contraction, while action potential is responsible for the contraction itself.

• Action potential occurs in neurons, while pacemaker potential occurs in muscle cells.

• Action potential is responsible for heart rhythm, while pacemaker potential is not.

• Pacemaker potential is slower than action potential.

What triggers the initial depolarization in cardiomyocytes?

• Opening of voltage-gated sodium channels

• Closing of potassium channels

• Opening of voltage-gated calcium channels

• Efflux of calcium ions

During the plateau phase, what balances the efflux of potassium ions?

• Influx of sodium ions

• Influx of magnesium ions

• Influx of calcium ions

• Efflux of chloride ions

Why is the plateau phase crucial for heart function?

• It increases the heart's electrical activity.

• It prevents heart muscle fatigue.

• It ensures complete blood ejection from heart chambers.

• It allows for rapid heart rate.

What happens when calcium channels close during the repolarization phase?

• The membrane potential becomes more positive.

• Potassium channels close.

• Sodium channels open.

• The membrane potential returns to resting state.

How often does the cardiomyocyte action potential occur in a cardiac cycle?

• Continuously

• Only during exercise

• Once per cycle

• Twice per cycle

What is the resting membrane potential of cardiomyocytes?

• Negative 90 millivolts

• Zero millivolts

• Positive 30 millivolts

• Positive 20 millivolts