Voltage gated channels

Resting Membrane Potential

  • The cell membrane at resting membrane potential has:
    • Activation gates of voltage-gated sodium ion channels: Closed
    • Inactivation gates of voltage-gated sodium ion channels: Open
    • Voltage-gated potassium ion channels: Closed

Initiation of Depolarization

  • Depolarization occurs due to:
    • A stimulus that makes the membrane potential more positive.
    • Causes voltage-gated sodium ion channels to begin to open.

Threshold and Sodium Ion Diffusion

  • As the membrane potential reaches threshold:
    • A large number of sodium channels open.
    • Sodium ions (a^+]) diffuse across the membrane, leading to depolarization.

Role of Voltage-Gated Potassium Ion Channels

  • Voltage-gated potassium ion channels begin to open, but at a slower rate than sodium channels.
    • Result: Greater influx of sodium ions than the efflux of potassium ions during initial depolarization.

Maximum Depolarization Phase

  • As the membrane potential approaches maximum depolarization:
    • Inactivation gates of the voltage-gated sodium ion channels start to close, decreasing sodium ion diffusion.
    • Potassium ion channels remain open; potassium ions (^+]) continue to diffuse out of the cell.

Hyperpolarization Phase

  • The increased permeability to potassium ions results in:
    • The membrane potential becoming slightly more negative than the resting potential.

Return to Resting Membrane Potential

  • After the voltage-gated potassium ion channels close:
    • Active transport mechanisms for sodium (a^+]) and potassium (^+]) ions reestablish the resting membrane potential.