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Which phase of the non-pacemaker action potential is characterized by a plateau due to calcium influx?

Phase 1

Phase 2

Phase 2 of the non-pacemaker action potential is characterized by a plateau phase, primarily due to the influx of calcium ions. During this phase, voltage-gated calcium channels open, allowing calcium to enter the cell. This influx counters the repolarizing effects of potassium efflux, which occurs simultaneously. The result is a prolonged depolarization that creates the characteristic plateau. This phase is crucial for muscle cells, including cardiac muscle cells, as it allows for a sustained contraction, ensuring effective pumping of blood. The balance of calcium entry and potassium exit during this plateau phase is essential for the heart's contraction and helps prevent tetanus, ensuring that the heart can rhythmically contract and relax.

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Phase 3

Phase 4

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