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nmdcat.online July 28, 2026

During laboratory investigation, it is noted that cardiac muscle cells possess action potentials with a pronounced “plateau” phase. This physiological adaptation is primarily caused by:

A. The rapid, massive influx of sodium ions
B. The slow, prolonged influx of extracellular calcium ions
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C. The immediate, rapid efflux of potassium ions
D. The complete closure of all ion channels

📝 Explanation

The plateau phase of the cardiac action potential is caused by the opening of slow voltage-gated L-type calcium channels. The influx of extracellular calcium balances the efflux of potassium, prolonging the depolarization and ensuring a long refractory period that prevents tetanus.

📖 Additional Information

  • The rapid, massive influx of sodium ions
  • The slow, prolonged influx of extracellular calcium ions
  • The immediate, rapid efflux of potassium ions
  • The complete closure of all ion channels

The plateau phase of the cardiac action potential is caused by the opening of slow voltage-gated L-type calcium channels. The influx of extracellular calcium balances the efflux of potassium, prolonging the depolarization and ensuring a long refractory period that prevents tetanus.

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