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Understanding Membrane and Action Potentials

Mar 21, 2025

Lecture Notes on Membrane Potential and Action Potential

Overview

  • The lecture discusses the changes in membrane potential of an axon over time.
  • Focus on a specific part of the axon, not the entire axon.
  • Graph Description:
    • Y-axis: Membrane potential.
    • X-axis: Time.
    • Colored Dots:
      • Purple: Sodium-Potassium Pump
      • Orange: Voltage-Gated Sodium Ion Channel
      • Green: Voltage-Gated Potassium Ion Channel

Key Concepts

Resting Membrane Potential

  • Initial Condition: The axon cannot send an impulse or generate action potential without a potential difference.
  • Mechanism:
    • Uses ATP to power the sodium-potassium pump.
    • Transports 3 sodium ions out and 2 potassium ions in.
    • Results in lower voltage inside and higher voltage outside, achieving -70 mV.
    • This state is called the resting membrane potential.

Action Potential

Depolarization

  • Stimulus Effect: Opens voltage-gated sodium ion channels.
  • Ion Movement: Sodium ions rush in from high to low concentration.
  • Result: Membrane potential inside becomes more positive.
  • Charge Flipping: Inside becomes more positive compared to outside.
  • Occurs up to +30 mV.

Repolarization

  • Voltage Change: At +30 mV, sodium channels close, potassium channels open.
  • Ion Movement: Potassium ions rush out, losing more positive ions inside.
  • Result: Inside becomes more negative; potential decreases.
  • Reaches: Approximately -70 to -80 mV.

Refractory Period

  • Definition: Time taken to return to resting membrane potential.
  • Characteristic: Axon is unresponsive to any stimulus during this time.
  • Importance: Ensures the axon cannot generate another action potential immediately.

Summary

  • Action Potential Process: Depolarization and repolarization create the signal sent along the axon.
  • Graph Importance: Visual representation of the changes in membrane potential over time.

These notes encapsulate the process of how an axon generates and propagates an action potential through changes in membrane potential, emphasizing the roles of specific ion channels and the sodium-potassium pump.

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