Nervous System: Action Potentials, Neurons, and Neurotransmission Study Guide

Q1. Match the descriptions to the correct phase of the action potential shown in the graph.

Background

Topic: Action Potentials in Neurons

This question tests your understanding of the phases of the action potential, including resting potential, depolarization, repolarization, and hyperpolarization, as well as the roles of different ion channels during these phases.

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, mainly due to potassium ions leaving the cell.

• Hyperpolarization: The membrane potential becomes more negative than the resting potential, often due to continued potassium efflux.

• Threshold: The critical level to which the membrane potential must be depolarized to initiate an action potential (usually around -55 mV).

• Voltage-Gated Sodium Channels: Open rapidly during depolarization, allowing Na+ influx.

• Voltage-Gated Potassium Channels: Open during repolarization, allowing K+ efflux.

Step-by-Step Guidance

1. Examine the labeled graph and identify the baseline (most negative) membrane potential. This is the resting potential phase, typically labeled at the start and end of the action potential.

2. Find the point where the membrane potential rapidly rises from negative toward positive values. This steep upward slope is the depolarization phase, caused by the opening of voltage-gated sodium channels and influx of Na+.

3. Locate the peak of the action potential (the highest point on the graph). This is where the membrane potential is most positive, and sodium channels begin to inactivate while potassium channels start to open.

4. After the peak, the membrane potential rapidly drops back toward negative values. This is the repolarization phase, due to K+ leaving the cell through voltage-gated potassium channels.

5. Notice if the membrane potential briefly becomes more negative than the resting potential after repolarization. This is the hyperpolarization phase, often called the "undershoot."

6. Match each letter (A-F) on the graph to the correct phase or event (e.g., resting potential, depolarization, threshold, etc.) based on their position and the changes in membrane potential.

Try solving on your own before revealing the answer!

Final Answer:

• A: Resting potential

• B: Depolarization reaches threshold

• C: Sodium ions rushing into cell (depolarization phase)

• D: Peak of action potential

• E: Repolarization phase (potassium ions rushing out)

• F: Hyperpolarization (membrane potential more negative than resting)

Each letter corresponds to a key event or phase in the action potential, as shown on the graph. Understanding these phases is crucial for grasping how neurons transmit electrical signals.