Transcript Conduction of a Nerve Impulse - The Norton Knatchbull School

L5
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An action potential is an abrupt but shortlived reversal of the resting potential of a
neurone.
It occurs at a specific point of the neurone.
The graph shows the electrical changes that
occur during a single action potential.
1.
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The action potential begins when a particular stimulus causes the
membrane at one part of the neurone suddenly to increase its
permeability to Na+ ions.
This is labelled A and happens because the stimulus has caused
voltage-sensitive Na+ gates in this part of the membrane to open.
As a result, Na+ ions diffuse rapidly into the neurone along their
electrochemical gradient, reducing the negativity inside that part of
the neurone.
In a positive feedback loop, this causes more and more voltagesensitive Na+ gates to open until the voltage difference across the
membrane reverses.
The highest positive membrane potential is the action potential
and this part of the membrane is now said to be depolarised.
2.
At a certain point, labelled B the
depolarisation of the membrane causes
the voltage-sensitive Na+ gates to close.
3.
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Shortly after the voltage-sensitive Na+ gates close, the
voltage-sensitive K+ gates open. This is labelled C.
The voltage-sensitive K+ gates open more slowly than the
voltage-sensitive Na+ gates and allow K+ ions to flow out of
the neurone, along their electrochemical gradient.
This outflow of K+ ions restores the resting potential in the
neurone. In a negative feedback loop, the outward movement
of K+ ions results in the closing of the voltage-sensitive K+
gates (labelled D).
There is a slight 'overshoot' in the movement of K+ ions,
which causes the membrane potential to become slightly
lower than its normal resting potential. This is called
hyperpolarisation and is labelled region E.
4.
After the resting potential has been
restored, sodium-potassium pumps move
Na+ ions out of the neurone and move K+
ions back into the neurone by active
transport.
Activity 8.3 Nerve Impulse Propagation
 Question 8.11
 Answer exam questions from SoW
Extension
 Extension 8.1 about ion channels and
episodic diseases
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A new action potential will only be generated
at the leading edge of the previous one;
Because the membrane behind it will be
recovering/incapable of transmitting an
impulse;
The membrane has to be repolarised and
return to resting potential before another
action potential can be generated;