Question

Following electrical depolarization of the myocardial cell membrane, which ion rushes in first and which ion rushes in later?

1) Sodium and Calcium
2) Potassium and Sodium
3) Calcium and Potassium
4) Sodium and Potassium

Answer 1

The first ion to enter the myocardial cell membrane upon depolarization is sodium (Na+), followed by calcium (Ca2+). Potassium (K+) ions exit later during repolarization.

Step-by-step explanation:

Following the electrical depolarization of the myocardial cell membrane, the ion that rushes in first is sodium (Na+), and the ion that rushes in later is calcium (Ca2+). As the membrane becomes permeable, Na+ enters the cell, leading to depolarization. Subsequently, as the action potential peaks, calcium ion channels open allowing Ca2+ to enter the cell, contributing to further depolarization during the plateau phase. After this, potassium (K+) ions flow out to return the cell to its resting potential, a process called repolarization.