How a Neuron Fires: Voltage-Gated Channels

Lesson notes

Key points

• At rest, a neuron's membrane sits near minus seventy millivolts, inside negative, maintained by the sodium-potassium pump and potassium leak channels.
• When a stimulus reaches threshold, voltage-gated sodium channels open and sodium rushes in, depolarising the membrane toward positive values.
• Sodium channels then inactivate while slower voltage-gated potassium channels open, so potassium leaves and the membrane repolarises.
• Inactivated sodium channels cannot reopen immediately, creating a refractory period that keeps the signal travelling in one direction.

Definitions

Absolute refractory period

Interval when Na+ channels are inactivated, so no new action potential can fire regardless of stimulus strength.

Takeaway: Na+ in depolarises; K+ out repolarises; inactivation sets direction.

Resting potentialDepolarisationRepolarisationRefractory period