Action potential

• Changes in membrane permeability lead to depolarisation and the generation of an action potential.
• Stimulus: Na+ channels open; membrane permeability to Na+ increases.
• Na+ diffuse into axon down electrochemical gradient, causing depolarisation.
• Depolarisation: if threshold potential reached, an action potential is generated.
• More voltage-gated Na+ channels open as depolarisation continues, causing more Na+ to diffuse in rapidly.
• Repolarisation: voltage-gated Na+ channels close.
• Voltage-gated K+ channels open; K+ diffuse out of axon.
• Hyperpolarisation: K+ channels slow to close so there’s a slight overshoot – too many K+ diffuse out.
• Resting potential is restored by Na+/K+ pump.