Question 1

Which of the following best describes the electrochemical equilibrium for potassium (K$$^+) $$ions across a cell membrane?

Accepted Answer

The osmotic force balances the electrostatic force, resulting in no net movement of K$$^+$$ ions and a stable membrane voltage.

Question 2

During an action potential, which event occurs first after the membrane reaches threshold?

Accepted Answer

Voltage-gated Na$$^+$$ channels open, causing a rapid influx of Na$$^+$$ ions.

Question 3

In a voltage clamp experiment, what does a negative current injected by the amplifier indicate?

Accepted Answer

An inward flow of positive ions (such as Na$$^+) $$into the cell.

Question 4

Which of the following statements about the reversal potential for sodium (Na$$^+) is $$correct?

Accepted Answer

It is the membrane potential at which there is no net flow of Na$$^+$$ ions across the membrane.

Question 5

If extracellular Na$$^+ is $$removed and replaced with an impermeant cation, what happens to the early inward current during a voltage clamp depolarization?

Accepted Answer

The early inward current disappears.

Question 6

Which equation correctly relates membrane current, conductance, and driving force for a specific ion?

Accepted Answer

$$I_{ion} = g_{ion} (V_{m} - E_{ion})$$

Question 7

What is the primary effect of myelination on action potential conduction in axons?

Accepted Answer

It increases conduction speed by reducing membrane capacitance and increasing membrane resistance.

Question 8

Tetrodotoxin (TTX) is used experimentally to block which type of current?

Accepted Answer

Voltage-gated Na$$^+$$ current

Question 9

During the falling phase of the action potential, which of the following is primarily responsible for the change in membrane potential?

Accepted Answer

Opening of voltage-gated K$$^+$$ channels and inactivation of Na$$^+$$ channels

Question 10

Which of the following best explains why action potentials are unidirectional along an axon?

Accepted Answer

Na$$^+$$ channel inactivation prevents immediate re-excitation of the membrane behind the action potential.

Question 11

A neuron is voltage clamped at a potential more positive than the Na$$^+$$ reversal potential. What is the direction of the Na$$^+$$ current?

Accepted Answer

Outward, because Na$$^+$$ ions flow out of the cell.

Question 12

Which of the following changes would most likely increase the amplitude of the peak Na$$^+$$ current during an action potential?

Accepted Answer

Increasing the extracellular Na$$^+$$ concentration

Question 13

Which of the following best describes the effect of tetraethylammonium (TEA) on membrane currents?

Accepted Answer

It blocks voltage-gated K$$^+$$ currents without affecting Na$$^+$$ currents.

Question 14

If the membrane potential is held at the K$$^+$$ equilibrium potential, what will be the net K$$^+$$ current?

Accepted Answer

Zero, because the electrical and chemical driving forces are balanced.

Question 15

Which of the following is a direct consequence of the time- and voltage-dependence of Na$$^+$$ and K$$^+$$ conductances during an action potential?

Accepted Answer

The action potential has a characteristic shape with a rapid rise and slower fall.

Question 16

Which of the following best explains why myelinated axons conduct action potentials faster than unmyelinated axons?

Accepted Answer

Myelin increases membrane resistance and decreases capacitance, allowing action potentials to jump between nodes of Ranvier.

Question 17

A mutation causes voltage-gated Na$$^+$$ channels to inactivate more slowly. What is the most likely effect on the action potential?

Accepted Answer

The action potential will be broader and last longer.

Question 18

Which of the following is the best definition of conductance in the context of membrane physiology?

Accepted Answer

The ease with which ions can flow through open channels, measured as the inverse of resistance.

Voltage-Dependent Membrane Permeability and Action Potentials

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