Which ion creates a positive charge within the myocardium?

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Multiple Choice

Which ion creates a positive charge within the myocardium?

Explanation:
The question is about what movement of ions makes the inside of cardiac muscle cells positive during depolarization. Calcium entering the cell during the plateau phase produces and sustains that positive interior, prolonging depolarization and enabling the heart muscle to contract. This contrasts with sodium, which drives the rapid initial upstroke of depolarization, but the sustained positive charge inside during the plateau is due to calcium influx through L-type channels. Potassium helps bring the cell back toward its resting negative state, and chloride plays a much smaller, different role.

The question is about what movement of ions makes the inside of cardiac muscle cells positive during depolarization. Calcium entering the cell during the plateau phase produces and sustains that positive interior, prolonging depolarization and enabling the heart muscle to contract. This contrasts with sodium, which drives the rapid initial upstroke of depolarization, but the sustained positive charge inside during the plateau is due to calcium influx through L-type channels. Potassium helps bring the cell back toward its resting negative state, and chloride plays a much smaller, different role.

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