Co-ordination

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Resting Potential

sodium potassium pump 

3 sodium out - 2 potassium in 

more potassium leakage channels - membrane more permeable to 

results in more sodium on outside + more postassium inside

overall more ions outside of the axon

inside of the membrane is negative in relation to the outside

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Reaction to stimulus

Stimulus causes Na voltage gated channels to open

influx of Na 

Depolarisation - reversal of change - now positive in inside relation to the outside +40mV = Action Potential

K voltage gated channels out

influx of K 

repolarises the axon 

hyperpolarisation - K channels stay open longer than needed

all channels shut

resting potential restored

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Propagation of Action Potential

The reversal of charge causes a localised current which causes the Na channels in the adjactent area to open, so the next section gets repolarised

the section behind - the K channels open so that bit gets repolarised then hyperpolarisared 

this delays the next action potential from being passed to close to the first 

the K channels then shut so that the resting potential is restored ready for next action potential

this way the action potential only moves in one direction - towards the axon terminals, otherwise it could span out in both directions

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Speed of an Action Potential

factors

Myelinated/unmyelinated - if there is not myelin then the action potential/localised current can jump from one node of ranvier to the other as myelin is an insulator = saltatory conduction

Diametre of an axon - only for unmyelinated because the charge meets less resitence as less is in contact with the membrane in relation to the amount of charge running through

Temperature - increases the rate of diffusion of ions through the cell membrane as ions have more KE so will move faster when channels open


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