Depolarization and Hyperpolarization in Neurons: Understanding Membrane Potential Changes

Introduction

Neurons maintain a resting membrane potential of approximately -70 mV, which is crucial for signal transmission in the nervous system. When exposed to certain chemicals or stimuli, neurons can undergo depolarization or hyperpolarization, altering their ability to generate action potentials.

This article will explore how changes in membrane potential affect neuronal function and evaluate the correctness of two given statements regarding depolarization and hyperpolarization.

Understanding Membrane Potential in Neurons

1. Resting Membrane Potential (-70 mV)

Neurons have a stable resting membrane potential maintained by:

• The sodium-potassium (Na⁺/K⁺) pump, which actively transports Na⁺ out and K⁺ in
• Leak channels, allowing passive diffusion of ions
• Negatively charged intracellular proteins, contributing to a negative resting charge

2. Depolarization (Becoming Less Negative, Excitatory Response)

• Occurs when the membrane potential moves closer to 0 mV.
• Example: If a chemical (X) shifts the membrane potential from -70 mV to -50 mV, it reduces the negative charge inside the cell.
• Depolarization increases neuron excitability, making it more likely to fire an action potential.

3. Hyperpolarization (Becoming More Negative, Inhibitory Response)

• Occurs when the membrane potential moves further away from 0 mV.
• Example: If a chemical (Y) shifts the membrane potential from -70 mV to -90 mV, the cell becomes more negative inside.
• Hyperpolarization reduces neuron excitability, making it less likely to fire an action potential.

Evaluating the Given Statements

Statement I:

“In a neuron at standard resting state of -70 mV, treatment with a chemical (X) induced intracellular potential -50 mV while when treated with another chemical (Y), it showed -90 mV. Given such a condition, we can say (X) induced depolarization, while (Y) induced hyperpolarization.”

✅ Correct.

• X induces depolarization (-70 mV to -50 mV) → Membrane potential becomes less negative.
• Y induces hyperpolarization (-70 mV to -90 mV) → Membrane potential becomes more negative.

Statement II:

“In a neuron at standard resting state of -70 mV, treatment with a chemical (X) induced intracellular potential -50 mV while when treated with another chemical (Y), it showed -90 mV. Given such a condition, we can say (Y) induced depolarization, while (X) induced hyperpolarization.”

Incorrect.

• The statement incorrectly reverses the effects of X and Y.
• Y (-90 mV) causes hyperpolarization, not depolarization.
• X (-50 mV) causes depolarization, not hyperpolarization.

Correct Answer:

Option 3: Statement I is correct but Statement II is incorrect.

Related Topics: Neuronal Signaling and Action Potentials

1. Role of Ion Channels in Membrane Potential Changes

• Depolarization is often caused by the opening of Na⁺ or Ca²⁺ channels, allowing positive ions to enter the cell.
• Hyperpolarization is usually caused by the opening of K⁺ or Cl⁻ channels, making the inside of the cell more negative.

2. Importance of Depolarization and Hyperpolarization in Nervous System Function

• Depolarization is necessary for neuron activation and signal transmission.
• Hyperpolarization prevents excessive neuron firing and helps maintain balance in the nervous system.

Conclusion

Understanding depolarization and hyperpolarization is essential for studying neuronal function, signal transmission, and neurological disorders. The correct answer to the question is Option 3, as Statement I is correct, but Statement II is incorrect.

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