Question

Which of the following changes would cause a shift in the membrane potential of a neuronal cell from -70 mV to -50 mV?

• A. A decrease in \( K^+ \) permeability
• B. An increase in \( Na^+ \) permeability
• C. An increase in \( K^+ \) permeability
• D. A decrease in \( Na^+ \) permeability

Hint:

The membrane potential is more depolarized when \( Na^+ \) permeability increases and more hyperpolarized when \( K^+ \) permeability increases.

Answer 1

The Correct Option is A, B

Step 1: Understanding membrane potential.
The membrane potential is influenced by the relative concentrations of ions across the cell membrane and the membrane's permeability to those ions. The resting membrane potential is primarily determined by \( K^+ \) permeability, and the action potential is influenced by \( Na^+ \) permeability.
Step 2: Analyzing the Options.
- (A) A decrease in \( K^+ \) permeability would reduce the influence of \( K^+ \) on the membrane potential, making the cell less negative, but not to the extent of a shift from -70 mV to -50 mV.
- (B) Correct. An increase in \( Na^+ \) permeability allows more \( Na^+ \) ions to enter the cell, causing depolarization and shifting the membrane potential toward a more positive value, closer to +50 mV.
- (C) An increase in \( K^+ \) permeability would hyperpolarize the cell and make it more negative, not less.
- (D) A decrease in \( Na^+ \) permeability would make the membrane potential more negative, not less.
Step 3: Conclusion.
Thus, the correct answer is (B).