Which sequence is correct for the stages of the electrical activity in the myocardium during depolarization and repolarization?

Which sequence is correct for the stages of the electrical activity in the myocardium during depolarization and repolarization?

• A. K+ channels open; depolarization; Ca2+ channels open; Na+ gates close; repolarization begins.
• B. Na+ gates open; Ca2+ channels close; slow Ca2+ channels open; K+ channels open; rapid depolarization.
• C. Na+ gates open; rapid depolarisation; Na+ gates close; slow Ca2+ channels open; Ca2+ channels close, K+ channels open (Repolarisation).
• D. Slow Ca2+ channels open; Na+ gates open; rapid depolarization; K+ channels close; repolarization.

Answer: (C)

The motor behind this sequence is how ion channels control the cardiac action potential. Na+ channels open first, causing a rapid depolarization as Na+ rushes into the cell. Once those Na+ channels inactivate and close, the slow Ca2+ (L-type) channels open, producing a plateau by letting Ca2+ enter and counteracting K+ loss. When the Ca2+ channels finally close and K+ channels open, the membrane potential falls back toward resting levels, completing repolarization. So the correct progression is: Na+ gates open leading to rapid depolarization, then Na+ gates close, slow Ca2+ channels open to sustain the plateau, Ca2+ channels close, and K+ channels open to drive repolarization.

The motor behind this sequence is how ion channels control the cardiac action potential. Na+ channels open first, causing a rapid depolarization as Na+ rushes into the cell. Once those Na+ channels inactivate and close, the slow Ca2+ (L-type) channels open, producing a plateau by letting Ca2+ enter and counteracting K+ loss. When the Ca2+ channels finally close and K+ channels open, the membrane potential falls back toward resting levels, completing repolarization.

So the correct progression is: Na+ gates open leading to rapid depolarization, then Na+ gates close, slow Ca2+ channels open to sustain the plateau, Ca2+ channels close, and K+ channels open to drive repolarization.