Q: Which of the following equations correctly represents the Nernst equation for the equilibrium potential of potassium (K\^+)?

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

Question 1

Which of the following best explains why action potentials are described as 'all-or-none' events?

Accepted Answer

Once the threshold is reached, an action potential of constant amplitude is generated, regardless of stimulus strength.

Question 2

A neuron is stimulated repeatedly at a high frequency. Which property of action potentials limits the maximum firing rate of the neuron?

Accepted Answer

The absolute refractory period

Question 3

During the rising phase of the action potential, which of the following best describes the movement of ions across the membrane?

Accepted Answer

Voltage-gated Na\^+ channels open, allowing Na\^+ influx

Question 4

Which of the following equations correctly represents the Nernst equation for the equilibrium potential of potassium (K\^+)?

Accepted Answer

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

Question 5

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

Accepted Answer

The action potential will be broader (longer duration).

Question 6

Which of the following best explains why myelination increases the conduction velocity of action potentials?

Accepted Answer

Myelination increases membrane resistance ($R_m$), reducing ion leakage and allowing faster propagation.

Question 7

If the extracellular concentration of Na\^+ is increased, what will happen to the peak of the action potential?

Accepted Answer

The peak will become more positive.

Question 8

During the relative refractory period, which of the following is true?

Accepted Answer

A stronger-than-normal stimulus is required to generate an action potential.

Question 9

Which of the following best describes the effect of increasing axon diameter on conduction velocity?

Accepted Answer

Conduction velocity increases because of decreased internal resistance.

Question 10

A researcher uses patch-clamp technique to study Na\^+ channels. She observes that the current through the channel stops even though the depolarizing voltage is maintained. What is the most likely explanation?

Accepted Answer

The Na\^+ channel has inactivated despite continued depolarization.

Question 11

Which of the following is the main reason that action potentials propagate without decrement along an axon?

Accepted Answer

The opening of voltage-gated Na\^+ channels ahead of the action potential regenerates the signal.

Question 12

At the peak of the action potential (around $+40$ mV), which of the following occurs?

Accepted Answer

Voltage-gated Na\^+ channels are inactivated and voltage-gated K\^+ channels are open.

Question 13

Which of the following best explains why the maximum frequency of action potentials is limited to about 1000 Hz?

Accepted Answer

The duration of the action potential is about 1 ms, setting a limit on how quickly another can be generated.

Question 14

Which of the following changes would most likely increase the speed of action potential conduction in a neuron?

Accepted Answer

Increasing the membrane resistance ($R_m$) by adding myelin

Question 15

A neuron is exposed to a drug that blocks voltage-gated K\^+ channels. What is the most likely effect on the action potential?

Accepted Answer

Repolarization will be delayed, resulting in a prolonged action potential.

Question 16

Which of the following best describes the code used by neurons to convey information, given that action potentials are stereotyped?

Accepted Answer

The frequency of action potentials

Question 17

Which of the following is required for the opening of voltage-gated Na\^+ channels during an action potential?

Accepted Answer

A depolarization of about 10 mV from the resting potential

Question 18

Which of the following best explains why larger diameter axons conduct action potentials faster than smaller diameter axons?

Accepted Answer

Larger diameter axons have lower internal resistance, allowing ions to move more easily.

Question 19

Which of the following is a direct consequence of the absolute refractory period?

Accepted Answer

A second action potential cannot be generated immediately after the first.

Action Potentials: Mechanisms, Properties, and Conduction in Neurons

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