Question 1

Which of the following best explains why the resting membrane potential of a neuron is typically negative?

Accepted Answer

The membrane is more permeable to potassium ions due to leak channels, allowing more K$$^+ to $$leave the cell than Na$$^+ to $$enter.

Question 2

During the rising phase of the action potential, which of the following events occurs first?

Accepted Answer

Voltage-gated sodium channels open, allowing Na$$^+ to $$rush into the cell.

Question 3

A patient is exposed to a toxin that prevents voltage-gated sodium channels from inactivating. What is the most likely effect on the action potential?

Accepted Answer

The cell will be unable to repolarize, and the action potential will be prolonged.

Question 4

Which type of ion channel is primarily responsible for the rapid depolarization phase of the action potential?

Accepted Answer

Voltage-gated sodium channels

Question 5

What is the main functional difference between graded potentials and action potentials?

Accepted Answer

Graded potentials can summate and decrease with distance, while action potentials are regenerated and do not decrease in size.

Question 6

Which of the following best describes the absolute refractory period?

Accepted Answer

It is the period when voltage-gated sodium channels are either open or inactivated, and no new action potential can be generated.

Question 7

A neuron is exposed to a drug that increases the permeability of the membrane to potassium ions at rest. What is the most likely effect?

Accepted Answer

The resting membrane potential will become more negative (hyperpolarized).

Question 8

Which of the following scenarios best illustrates the function of a ligand-gated ion channel?

Accepted Answer

A neurotransmitter binds to a receptor, causing the channel to open and ions to flow across the membrane.

Question 9

Which of the following best explains why action potentials only travel in one direction along an axon?

Accepted Answer

Voltage-gated sodium channels behind the action potential are inactivated, creating a refractory period.

Question 10

A graded potential fails to reach threshold at the trigger zone. What is the most likely outcome?

Accepted Answer

No action potential will occur.

Question 11

Which of the following equations best represents the Nernst equation for calculating the equilibrium potential for potassium ($$K^+$$)?

Accepted Answer

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

Question 12

Which of the following is a direct result of the opening of voltage-gated potassium channels during an action potential?

Accepted Answer

The cell repolarizes as K$$^+$$ exits the cell.

Question 13

A patient has a mutation that causes voltage-gated sodium channels to open at a more negative membrane potential than normal. What is a likely consequence?

Accepted Answer

The neuron will fire action potentials more easily, possibly leading to hyperexcitability.

Question 14

Which of the following best describes the sequence of events during an action potential?

Accepted Answer

Depolarization, repolarization, hyperpolarization, return to rest

Question 15

Which of the following is true regarding leak channels in the neuronal membrane?

Accepted Answer

They allow ions to move down their concentration gradients, contributing to the resting membrane potential.

Question 16

Which of the following best explains why the sodium-potassium pump is essential for neuronal function?

Accepted Answer

It maintains the Na$$^+$$ and K$$^+$$ gradients necessary for action potentials by pumping 3 Na$$^+$$ out and 2 K$$^+ in $$per ATP hydrolyzed.

Question 17

A neuron is exposed to a drug that blocks all voltage-gated potassium channels. What is the most likely effect on the action potential?

Accepted Answer

The depolarization phase will be prolonged, and repolarization will be greatly delayed.

Question 18

Which of the following is a property of the relative refractory period?

Accepted Answer

Some sodium channels have reset, but potassium permeability remains elevated, so a stronger stimulus is required to fire another action potential.

Question 19

Which of the following best describes the effect of a depolarizing graded potential that does not reach threshold?

Accepted Answer

It will summate with other potentials but will not cause an action potential by itself.

Question 20

Which of the following is the correct sequence for the states of a voltage-gated sodium channel during an action potential?

Accepted Answer

Closed → Open → Inactivated → Closed

The Action Potential: Mechanisms and Dynamics in Excitable Cells

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