Q: Which equation best describes the Nernst potential for potassium ($$\mathrm{K^+}) $$during the resting phase (A)?

$$E_{K^+} = \frac{RT}{zF} \ln \left( \frac{[K^+]_{\text{outside}}}{[K^+]_{\text{inside}}} \right)$$

Question 1

Refer to the action potential graph provided. Which phase is represented by label 'A', and what is the primary ion movement responsible for this phase?

Accepted Answer

Resting potential; maintained by potassium efflux

Question 2

At which labeled point does the membrane potential reach threshold, and what is the significance of this event?

Accepted Answer

C; triggers opening of voltage-gated sodium channels

Question 3

Which phase (label) corresponds to the rapid depolarization of the neuron, and which ion is primarily responsible?

Accepted Answer

C; sodium ($$\mathrm{Na^+}) $$influx

Question 4

What event is occurring at label 'D', and what is the approximate membrane potential at this point?

Accepted Answer

Peak of action potential; $$+30 mV$$

Question 5

Label 'E' represents which phase of the action potential, and what is the main ion movement?

Accepted Answer

Repolarization; potassium ($$\mathrm{K^+}) $$efflux

Question 6

What is the physiological significance of the phase labeled 'F'?

Accepted Answer

It represents the refractory period, during which a new action potential cannot be initiated.

Question 7

Which labeled phase is most directly associated with the opening of voltage-gated potassium channels?

Accepted Answer

E

Question 8

During which phase does the membrane potential become more negative than the resting potential, and what is this phase called?

Accepted Answer

F; hyperpolarization

Question 9

If a neuron is exposed to a toxin that blocks voltage-gated sodium channels, which phase(s) of the action potential would be directly affected?

Accepted Answer

C and D

Question 10

Suppose a mutation causes potassium channels to remain open longer than normal. How would this affect the action potential graph?

Accepted Answer

The hyperpolarization phase (F) would be prolonged and more negative.

Question 11

Which equation best describes the Nernst potential for potassium ($$\mathrm{K^+}) $$during the resting phase (A)?

Accepted Answer

$$E_{K^+} = \frac{RT}{zF} \ln \left( \frac{[K^+]_{	ext{outside}}}{[K^+]_{	ext{inside}}} ight)$$

Question 12

If the extracellular sodium concentration is decreased, what effect would this have on the peak of the action potential (D)?

Accepted Answer

The peak would be lower because less sodium enters the cell during depolarization.

Action Potential Phases and Neuronal Physiology

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