Phases Of Action Potential

Explanation
During the rapid depolarization phase (Phase 0) of an action potential, the correct answer states that sodium (Na) ions flood into the cell. This is because during Phase 0, the cell membrane rapidly becomes more positive as sodium channels open and allow sodium ions to rush into the cell. This influx of positive ions causes the membrane potential to rapidly depolarize, leading to the initiation of an action potential.

Explanation
Phase 2 of the cardiac action potential is known as the plateau phase. During this phase, there is a slow inward movement of calcium ions and an outward movement of potassium ions. This balance between calcium and potassium ions helps to maintain the depolarized state of the cell membrane, prolonging the action potential and allowing for sustained contraction of the cardiac muscle. This phase is important for the efficient pumping of blood by the heart.

Explanation
Phase 3 of cardiac action potential is characterized by rapid repolarization, which refers to the end of sodium and calcium inflow and the rapid outward movement of potassium ions. During this phase, the potassium channels open, allowing potassium ions to move out of the cell, which leads to the restoration of the cell's resting membrane potential. This repolarization prepares the cell for the next action potential and allows for proper cardiac rhythm and function.

Explanation
In phase 4 of the cardiac action potential, the resting membrane potential is maintained. This is achieved by having a large permeability to potassium ions, which allows for the net loss of intracellular potassium. This loss of positive charge contributes to the negative resting membrane potential.