Action Potential Phases and Neuronal Physiology

Q1. Match the descriptions to the correct phase of the action potential in the diagram above. Some letters will be used more than once.

Background

Topic: Action Potential Phases in Neurons

This question tests your understanding of the different phases of the action potential in a neuron, including the changes in membrane potential and the ion channel activity that underlies each phase.

Key Terms and Concepts:

• Resting Potential: The baseline membrane potential of a neuron, typically around -70 mV.

• Depolarization: The phase where the membrane potential becomes more positive due to sodium ions entering the cell.

• Repolarization: The phase where the membrane potential returns toward the resting value, usually due to potassium ions leaving the cell.

• Hyperpolarization: The membrane potential temporarily becomes more negative than the resting potential.

• Threshold: The critical level to which the membrane potential must be depolarized to initiate an action potential.

• Voltage-Gated Ion Channels: Channels that open or close in response to changes in membrane potential.

Step-by-Step Guidance

1. Examine the labeled points (A–F) on the graph. Identify the resting membrane potential (usually the flat region before any rapid change in voltage).

2. Find the point where the membrane potential rapidly rises (depolarization). This is typically due to the opening of voltage-gated sodium channels and sodium ions rushing into the neuron.

3. Locate the peak of the action potential (the highest point on the graph). This is where the inside of the neuron is most positive relative to the outside.

4. Identify the phase where the membrane potential rapidly falls (repolarization). This is usually due to potassium ions leaving the cell through voltage-gated potassium channels.

5. Look for the phase where the membrane potential dips below the resting potential (hyperpolarization) before returning to baseline.

6. Match each description (e.g., sodium ions rushing in, potassium channels opening, resting potential, etc.) to the appropriate lettered phase on the graph. Use your knowledge of the sequence of events in an action potential to guide your choices.

Try solving on your own before revealing the answer!

Final Answer:

• Resting potential: E

• Voltage-gated potassium channels open: A

• Depolarization phase: D

• Sodium ions rushing into cell: C

• Hyperpolarization: F

• Depolarization reaches threshold: B

• Repolarization phase: F

Each phase of the action potential corresponds to specific ion movements and channel openings/closings, as shown in the graph. Understanding these phases is crucial for mastering neuronal physiology.