CVS Practice Test

The resting cell membrane of the myocardial cell is relatively permeable to which ion?

1. Sodium

2. Calcium

3. Potassium

4. Chloride

The correct answer is: Potassium

The resting cell membrane of myocardial cells is relatively permeable to potassium ions. This permeability is essential for maintaining the resting membrane potential, which is primarily determined by the distribution of potassium ions both inside and outside the cell. At rest, there is a higher concentration of potassium ions inside the cell compared to the extracellular environment. As potassium ions move out of the cell through potassium channels, it creates a negative charge inside relative to the outside, thus stabilizing the resting membrane potential. This negative resting potential is crucial for the cell’s excitability and is a key factor in the generation and conduction of electrical impulses in the heart, facilitating coordinated contractions of the cardiac muscle. The other ions listed, while important in cardiac physiology, do not significantly influence the resting membrane potential in the same way that potassium does. Sodium and calcium play more prominent roles during depolarization and the action potential phase of myocardial activity, while chloride ions primarily have a minor role in membrane potential dynamics.