Question 1

Which of the following best describes the Nernst potential ($$E_{ion}) $$for a given ion across a cell membrane?

Accepted Answer

It is the membrane potential at which the net flux of that ion is zero due to a balance between its concentration gradient and electrical gradient.

Question 2

A neuron has an internal potassium concentration of 140 mM and an external concentration of 4 mM. Using the Nernst equation at 37°C, which formula would you use to calculate the equilibrium potential for potassium ($$E_K$$)?

Accepted Answer

$$E_K = \frac{RT}{zF} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$$

Question 3

If the membrane potential ($$V_m) is $$more negative than the Nernst potential for sodium ($$E_{Na}$$), what will be the direction of sodium ion movement if sodium channels open?

Accepted Answer

Sodium ions will move into the cell.

Question 4

Which of the following statements about the Goldman-Hodgkin-Katz (GHK) equation is correct?

Accepted Answer

It calculates membrane potential by considering the relative permeabilities and concentrations of multiple ions.

Question 5

A cell membrane is only permeable to potassium. If the external potassium concentration increases, what happens to the Nernst potential for potassium ($$E_K$$)?

Accepted Answer

It becomes less negative (moves closer to zero).

Question 6

Which of the following is a primary function of the Na+/K+ ATPase pump in excitable cells?

Accepted Answer

Maintaining the concentration gradients of Na+ and K+ across the membrane by active transport.

Question 7

A neuron’s membrane potential is at -70 mV, and the Nernst potential for chloride ($$E_{Cl}) is -65 mV. If $$chloride channels open, what is the expected direction of chloride ion movement?

Accepted Answer

Chloride ions will move out of the cell.

Question 8

Which equation would you use to calculate the equilibrium potential for an ion X with charge $$z$$ and concentrations $$[X]_{out}$$ and $$[X]_{in} at $$temperature $$T$$?

Accepted Answer

$$E_X = \frac{RT}{zF} \ln \left( \frac{[X]_{out}}{[X]_{in}} \right)$$

Question 9

During an action potential, the membrane potential rapidly approaches the Nernst potential for sodium ($$E_{Na}). $$What does this indicate about the membrane’s permeability?

Accepted Answer

The membrane has become highly permeable to sodium ions.

Question 10

If a cell’s membrane potential ($$V_m) is $$equal to the Nernst potential for potassium ($$E_K$$), what is the net movement of potassium ions?

Accepted Answer

There is no net movement of potassium ions.

Question 11

Which of the following best explains why the resting membrane potential of a neuron is closer to the Nernst potential for potassium than for sodium?

Accepted Answer

The membrane is more permeable to potassium than to sodium at rest.

Question 12

A mutation causes a neuron’s potassium leak channels to become nonfunctional. What is the most likely effect on the resting membrane potential?

Accepted Answer

The resting membrane potential will become less negative.

Question 13

Which of the following is TRUE regarding the effect of temperature on the Nernst equation?

Accepted Answer

Increasing temperature increases the magnitude of the equilibrium potential.

Question 14

A cell is permeable to both sodium and potassium. If the permeability to sodium increases dramatically, what happens to the membrane potential?

Accepted Answer

It moves closer to the Nernst potential for sodium ($$E_{Na}).$$

Question 15

Which of the following is NOT a property of ion channels in excitable cells?

Accepted Answer

They require ATP hydrolysis to open.

Question 16

A patient is given a drug that blocks all sodium channels in neurons. What is the most immediate effect on neuronal signaling?

Accepted Answer

Action potentials cannot be generated.

Question 17

Which of the following best describes depolarization in a neuron?

Accepted Answer

A decrease in the difference between inside and outside membrane potential, making the inside less negative.

Question 18

If the concentration of an ion is equal inside and outside the cell, what is its Nernst potential?

Accepted Answer

Zero millivolts ($$0 mV)$$

Question 19

Which of the following scenarios would result in hyperpolarization of a neuron?

Accepted Answer

Opening of potassium channels causing K+ to leave the cell.

Excitable Cells: Membrane Potentials, Nernst & GHK Equations

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