NEURON ACTION POTENTIAL (MADE EASY)

Study Guide: Action Potential (Nerve Impulse)

Overview

  • An action potential is a wave of depolarization and repolarization that occurs across the cell membrane of a neuron, similar to ripples on a pond.

Key Components

  • Cell Membrane Channels: Neurons contain thousands of tiny channels that allow the passage of ions (sodium and potassium).

  • Resting State:

    • Neurons generally have closed channels in a resting state.

    • The inside of the cell membrane is more negative than the outside, with a resting membrane potential of about -70 millivolts (mV).

  • Polarized Membrane: The electrical difference across the membrane makes it polarized.

Triggering an Action Potential

  • A nerve impulse is initiated when sensory inputs disturb the neuron's membrane, reaching a threshold voltage of about -55 mV.

  • Depolarization:

    • At this threshold, sodium channels open, allowing sodium ions (Na⁺) to flow into the cell.

    • This influx of positive ions causes the inside of the membrane to become less negative, leading to depolarization (the membrane potential rises).

Sequence of Ion Movement

  1. Depolarization: Inside of the axon changes from negative to positive as Na⁺ enters.

  2. Repolarization: After depolarization, potassium channels open, allowing potassium ions (K⁺) to exit the neuron, restoring a negative charge inside the axon.

  3. Hyperpolarization: Some potassium channels remain open, causing the inside of the cell to become more negative than the resting state.

Refractory Period

  • After an action potential, the neuron enters a refractory period where it cannot conduct another impulse. During this time:

    • The sodium-potassium pump works to return Na⁺ outside and K⁺ inside the neuron, restoring resting potential.

Summary

  • An action potential is a complex process of depolarization and repolarization, involving the coordinated opening and closing of voltage-gated ion channels and is essential for neuronal communication.