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Title: Action Potentials
Description: Summary about how an action potential is generated. A2 level biology.
Description: Summary about how an action potential is generated. A2 level biology.
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Action Potential
• If an electrical current above a threshold level is applied to the membrane it causes a massive
change in the potential difference
• Potential difference reversed
• Inside of axon positive and outside negative —> depolarisation
• Potential difference becomes about 40mV for about 3ms
• Membrane returns to resting potential as soon as possible —> more impulses can be
conducted —> repolarisation
• The large change in the voltage across the membrane is known as action potential
What causes an action potential?
1
...
There is a change in permeability to
sodium ions and potassium ions
...
This makes
the inside of the neurone less negative
...
As this happens the membrane
depolarises - the resting potential of the
cell starts to decrease
...
4
...
5
...
The membrane is more permeable to potassium so potassium
ions diffuse out of the neurone down the potassium ion concentration gradient
...
—> Repolarisation
6
...
The potential difference becomes more negative
than the resting potential
...
The ion channels are reset
...
8
...
This is because the ion channels are recovering and they can’t be made to open - sodium
1
ion channels are closed during repolarisation and potassium ion channels are closed during
hyperpolarisation
...
9
...
How is the impulse passed along the axon?
• Action potential generated does not actually travel along the axon —> triggers a sequence of
action potentials along the length of the axon
• When part of membrane becomes depolarised at the site of an action potential, a local
electrical current is created as the charged sodium ions flow between the depolarised part of
the membrane and the adjacent resting region,
• Depolarisation spreads to adjacent region and nearby sodium ion channels open, triggering
another resting potential
• As a result, a wave of depolarisation will pass along the membrane —> nerve impulse
2
Title: Action Potentials
Description: Summary about how an action potential is generated. A2 level biology.
Description: Summary about how an action potential is generated. A2 level biology.