What are the three phases of the cardiac myocyte action potential?

Phase 0—depolarization because of the opening of fast sodium channels. Potassium flux also decreases. Phase 1—partial repolarization because of a rapid decrease in sodium ion passage as fast sodium channels close. Phase 2—plateau phase in which the movement of calcium ions out of the cell, maintains depolarization.

How long does a cardiac action potential last?

In a typical nerve, the action potential duration is about 1 ms. In skeletal muscle cells, the action potential duration is approximately 2-5 ms. In contrast, the duration of cardiac action potentials ranges from 200 to 400 ms.

What happens when the heart Depolarizes?

Depolarization of the heart is the orderly passage of electrical current sequentially through the heart muscle, changing it, cell by cell, from the resting polarized state to the depolarized state until the entire heart is depolarized. What is meant by repolarization of the heart muscle?

What happens in Phase 4 of action potential?

Phase 4 is the spontaneous depolarization (pacemaker potential) that triggers the action potential once the membrane potential reaches threshold between -40 and -30 mV). As ions flow through open channels, they generate electrical currents that change the membrane potential.

What happens during a cardiac action potential?

The cardiac action potential is a brief change in voltage (membrane potential) across the cell membrane of heart cells. This is caused by the movement of charged atoms (called ions) between the inside and outside of the cell, through proteins called ion channels.

Does depolarization mean relaxation?

When the electrical signal of a depolarization reaches the contractile cells, they contract. When the repolarization signal reaches the myocardial cells, they relax. Thus, the electrical signals cause the mechanical pumping action of the heart.

Is depolarization the same as contraction?

The P wave represents depolarization of the atria and is followed by atrial contraction (systole). Atrial systole extends until the QRS complex, at which point, the atria relax. The QRS complex represents depolarization of the ventricles and is followed by ventricular contraction.

Is depolarization a contraction?

Atrial depolarization initiates contraction of the atrial musculature. As the atria contract, the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular (AV) valves, leading to a rapid flow of blood into the ventricles.

Which drug increases duration of the action potential by prolonging repolarization in phase 3?

Potassium-channel blockers delay phase 3 repolarization, thereby lengthening the action potential duration and ERP.

What is the action potential of the cardiac ion channel?

Phase 0 is the phase of rapid depolarization. The membrane potential shifts into positive voltage range. This phase is central to rapid propagation of the cardiac impulse (conduction velocity, θ=1 m/s). Phase 1 is a phase of rapid repolarization. This phase sets the potential for the next phase of the action potential.

Is the action potential of the myocardium a wave?

Note that the terms electrical impulse, impulse and impulse wave are used interchangeably to refer to the wave-like spread of the action potential in the myocardium. Figure 3. The action potential of contractile cells.

How does the spread of the cardiac action potential propagate?

Movement of electrically charged particles – which occur during spread of the cardiac action potential – generates an electrical vector. The depolarization propagates through the myocardium similar to the spread of a wave front in water.

When does the cardiac myocyte action potential plummet?

After myocyte contraction has occurred in phase 2, the action potential will then “plummet” again as the voltage across the cell membrane becomes negative. This is referred to as repolarization and is phase 3 of the cardiac myocyte action potential. We know from phase 1 that plummeting will involve the efflux of potassium ions.