Overview
This lecture explains how voltage-gated ion channels function to create and reset action potentials in neurons by regulating sodium and potassium ion flow.
Voltage-Gated Ion Channels Basics
- Voltage-gated ion channels open or close in response to changes in the cell membrane potential.
- There are voltage-gated sodium (Na⁺) channels and voltage-gated potassium (K⁺) channels.
- At rest, these channels are closed, maintaining the resting membrane potential.
Resting Membrane Potential
- The resting membrane potential is set up by the sodium-potassium ATPase pump (see previous tutorial).
- The outside of the cell (extracellular) has more positive charges; the inside (intracellular) is more negative.
Action Potential Generation
- A change in membrane voltage opens the sodium channels, allowing Na⁺ to flow into the cell.
- Influx of Na⁺ ions makes the inside of the cell more positive (depolarization).
- Potassium channels also open in response to the voltage change, but with a delay.
- When potassium (K⁺) channels open, K⁺ leaves the cell, making the inside more negative (repolarization).
Channel Closing Mechanisms
- Sodium channels quickly close using a "ball and chain" inactivation mechanism.
- Potassium channels close after a short delay, stopping the flow of K⁺.
Action Potential Recording
- Changes in membrane voltage over time produce a characteristic action potential graph.
- Depolarization occurs as sodium enters; repolarization follows as potassium exits.
- After both channels close, the membrane potential returns to its resting state.
Key Terms & Definitions
- Voltage-Gated Channel — a protein channel that opens or closes in response to changes in membrane potential.
- Resting Membrane Potential — the baseline electrical charge difference across the cell membrane.
- Depolarization — the process of the cell becoming more positive inside due to Na⁺ influx.
- Repolarization — the return to a more negative membrane potential as K⁺ exits.
- Ball and Chain Mechanism — a method by which sodium channels are quickly inactivated.
Action Items / Next Steps
- Review how sodium-potassium ATPase establishes resting membrane potential (see previous tutorial).
- Watch the next video on action potential propagation along axons.