Suppose the change in Vm was caused by the entry of Ca^2+ instead of Na^+ . How many Ca^2+ ions

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Suppose the change in Vm was caused by the entry of Ca^2+...

Suppose the change in $V_{m}$ was caused by the entry of $\mathrm{Ca}^{2+}$ instead of $\mathrm{Na}^{+} .$ How many $\mathrm{Ca}^{2+}$ ions would have to enter the cell per unit membrane to produce the change? A. Half as many as for $\mathrm{Na}^{+}$ B. The same as for $\mathrm{Na}^{+}$ C. Twice as many as for Na^{+} D. Cannot say without knowing the inside and outside concentrations of $C a^{2+}$

Suppose the change in $V_{m}$ was caused by the entry of $\mathrm{Ca}^{2+}$ instead of $\mathrm{Na}^{+} .$ How many $\mathrm{Ca}^{2+}$ ions would have to enter the cell per unit membrane to produce the change?

A. Half as many as for $\mathrm{Na}^{+}$
B. The same as for $\mathrm{Na}^{+}$
C. Twice as many as for Na^{+}
D. Cannot say without knowing the inside and outside concentrations of $C a^{2+}$

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Key Concepts

Membrane Potential

This concept refers to the electrical potential difference across the cell membrane, which is established by the distribution of ions on either side of the membrane. Changes in membrane potential occur due to the movement of charged particles (ions) across the membrane, which alters the net charge difference between the intracellular and extracellular environments.

Ion Valence (Charge of Ions)

Ion valence represents the number of charges an ion carries. In this context, Ca²? carries two positive charges compared to Na? which carries a single positive charge. This difference is critical because each Ca²? ion delivers twice the charge of a Na? ion, meaning that for an equivalent change in membrane potential, fewer Ca²? ions are needed.

Charge Equivalence and Quantitative Comparison

This concept involves calculating the amount of ionic movement required to achieve a change in membrane potential based on the charge contributed by each ion. Since Ca²? ions contribute double the charge per ion relative to Na? ions, it follows that only half as many Ca²? ions need to enter the cell compared to Na? ions to produce the same change in potential.

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