At first, the neurone is at rest. The sodium potassium pump uses ATP to actively transport 3 sodium ions out and 2 potassium ions in. Gated sodium channels are closed. The neurone is polarised at -70mV., When a nerve impulse is stimulated, a small number of voltage gated sodium ion channels open, allowing sodium to diffuse in., This means the neurone becomes less negative - a potential difference of -50mV., When this threshold of -50mV is reached, the rest of the gated sodium ion channels open, causing rapid diffusion of sodium into the axon - depolarisation., This makes the inside of the neurone more positive than the outside with a potential difference of +40mV., Sodium ion channels now close and potassium ion channels open, causing potassium to flood out of the cell., This makes the inside of the neurone more negative again - repolarisation., If the repolarisation goes beyond -70mV the membrane is said to be hyperpolarised, there is a recovery period (called the refractory period) in which no further action potentials can occur while the resting membrane potential is being establised..

Action potential order

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