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Title: Passage of an Action Potential
Description: These are A level notes of the passage of an action potential. It gives details on the resting potential and the different stages of polarisation and depolarisation as well as the 'All or Nothing Principle'.
Description: These are A level notes of the passage of an action potential. It gives details on the resting potential and the different stages of polarisation and depolarisation as well as the 'All or Nothing Principle'.
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PASSAGE OF AN
ACTION POTENTIAL
Resting Potential
■ High concentration of sodium ions (Na+) outside axon membrane compared to
inside
■ High concentration of potassium ions (K+) inside membrane
■ Concentration of positive ions is greater on the outside
■ Axon membrane = polarised
■ Stimulus causes a sudden influx of sodium ions
■ This causes a reversal of charge on the axon membrane – action potential
■ Influx → establishes localised electrical currents
→ opens sodium voltage – gated channels a little further along the axon
■ More sodium ions come through this area, causing depolarisation
■ Behind this depolarisation, the sodium voltage – gated channels close and the potassium
ones open
■ Potassium ions begin to leave the axon along their electrochemical gradient
■ Once initiated, the depolarisation moves along the membrane
■ Action potential (depolarisation) moves the same way along the axon
■ The outward movement of potassium ions continues until the point where the axon
membrane has returned to its original, charged state (positive outside and negative inside)
■ Meaning it has been re – polarised
■ The axon being polarised means sodium ions can be actively transported out
■ The axon then returns to its resting potential, ready in case a new stimulus comes along
All or Nothing Principle
■ Threshold not reached = action potential won’t fire
■ Once threshold is reached an action potential will always fire with the same change
in voltage no matter the size of the stimulus
Title: Passage of an Action Potential
Description: These are A level notes of the passage of an action potential. It gives details on the resting potential and the different stages of polarisation and depolarisation as well as the 'All or Nothing Principle'.
Description: These are A level notes of the passage of an action potential. It gives details on the resting potential and the different stages of polarisation and depolarisation as well as the 'All or Nothing Principle'.