Question 1

Which equation would you use to calculate the equilibrium potential for a single ion species across a membrane, and what is the general form of this equation?

Accepted Answer

The Nernst Equation: $$E_X = \frac{RT}{zF} \ln \frac{[X]_{out}}{[X]_{in}}$$

Question 2

A neuron has an intracellular K$$^+$$ concentration of 140 mM and an extracellular K$$^+$$ concentration of 5 mM. Using the simplified Nernst equation at 18°C ($$E_K = 58 \log_{10} \frac{[K^+]_{out}}{[K^+]_{in}}$$), what is the equilibrium potential for K$$^+$$?

Accepted Answer

$$E_K = -90 mV$$

Question 3

Which of the following best describes the movement of ions at electrochemical equilibrium?

Accepted Answer

There is no net movement of ions because the electrical and chemical gradients are balanced.

Question 4

If the membrane potential ($$V_m) is $$set to a value more negative than the equilibrium potential for K$$^+$$ ($$E_K$$), what will be the direction of net K$$^+$$ flux?

Accepted Answer

K$$^+$$ will flow into the cell.

Question 5

Which of the following is a limitation of the Nernst equation when predicting the resting membrane potential?

Accepted Answer

It does not account for the relative permeability of multiple ions.

Question 6

What is the main difference between the IV (current-voltage) relationship for cations and anions?

Accepted Answer

For cations, inward current is negative; for anions, inward current is positive.

Question 7

Given the following ion concentrations in a mammalian neuron: $$[Na^+]_{in} = 15 mM$$, $$[Na^+]_{out} = 145 mM$$, what is the equilibrium potential for Na$$^+ at 18$$°C using the simplified Nernst equation?

Accepted Answer

$$E_{Na} = +60 mV$$

Question 8

When should you use the Goldman Equation instead of the Nernst Equation?

Accepted Answer

When multiple ions with different permeabilities contribute to the membrane potential.

Question 9

What is the driving force for an ion, and how is it calculated?

Accepted Answer

The difference between the membrane potential and the equilibrium potential for that ion: $$DF = V_m - E_x$$

Question 10

A cell membrane is only permeable to Na$$^+. $$What will the membrane potential ($$V_m) be$$?

Accepted Answer

$$V_m = E_{Na}$$

Question 11

Which of the following best explains why the resting membrane potential of a neuron is typically closer to $$E_K$$ than $$E_{Na}$$?

Accepted Answer

The membrane is more permeable to K$$^+$$ than to Na$$^+ at $$rest.

Question 12

If the membrane potential ($$V_m) is +50 mV $$and $$E_K is -90 mV$$, what is the driving force for K$$^+$$?

Accepted Answer

$$DF = +140 mV$$

Question 13

Which of the following scenarios would result in no net flux of K$$^+$$ across a membrane permeable only to K$$^+$$?

Accepted Answer

When $$V_m = E_K$$

Question 14

What is the effect on the membrane potential if the permeability to Na$$^+$$ increases while K$$^+$$ permeability remains constant?

Accepted Answer

The membrane potential will shift toward $$E_{Na}.$$

Question 15

Which of the following best describes the role of active transporters in maintaining ion gradients?

Accepted Answer

They move ions against their concentration gradients using energy.

Question 16

A cell has the following permeabilities: $$P_{K^+} = 1$$, $$P_{Na^+} = 0.05$$, $$P_{Cl^-} = 0.45. $$Which equation should be used to calculate the membrane potential?

Accepted Answer

The Goldman-Hodgkin-Katz (Goldman) equation

Question 17

If the membrane potential is set to 0 mV in a cell with $$E_K = -58 mV$$, what will be the direction of net K$$^+$$ flux?

Accepted Answer

K$$^+$$ will flow out of the cell.

Question 18

Which of the following is NOT a typical equilibrium potential value for ions in a mammalian neuron?

Accepted Answer

$$E_{Na} = -90 mV$$

Ionic Basis of the Resting Membrane Potential: Study Guide

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