Hyperpolarisation

• After action potential is achieved with maximum potential difference of +40mV, Na+ voltage gated channels close and K+ voltage gated channels open
• More and more K+ ions diffuse out of neurone, down an electrochemical gradient, causing fall in potential difference across neurone, restoring negative potential difference
• There is slight K+ ion overshoot as too many ions diffuse out of neurone, causing PD to be more negative than normal resting value; e.g -75mV, membrane is now hyper polarised
• Although resting potential is almost correct value, Na+ and K+ ions are on opposite sides, so action potential cannot occur until they are pumped to correct positions on either side (more Na+ ions outside, and more K+ ions inside)
• Refractory potential: Time taken (milliseconds) after action potential peak to establish true axon resting potential, adjusts Na+ and K+ ions to correct positions, so membrane is resting and polarised