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D
Action potentials
1.3 Converting energy into nerve impulses, resting potentials and action potentials

Sensory receptors
A receptor converts an external or internal stimulus into an electrical signal. Sensory receptors detect changes in their
surroundings. The table below outlines the main stimuli and the receptors which detect them:

Stimulus Receptor…

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Triggering an action potential
Because the number of sodium ions which can enter the cell during the process varies so greatly, sometimes there is only
a small depolarisation, where the result is only a slight increase in voltage across the membrane. This small depolarisation
is known as a generator potential.…

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Events of an action potential
Now that you understand the behaviour of a neural membrane at its resting state and you know what causes an action
potential to be generated, you should be able to understand the events of a single action potential. Action potentials are
triggered by ionic movements…

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Transmission of an action potential
The resting neurone has a stable balance of sodium and potassium ions, which is created by the sodium-potassium pump.
The ions are sorted so that there are mainly sodium ions outside the cell and mainly potassium ions inside the cell, also so
that the inside…

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The myelinated sheath won't allow sodium or potassium ions to diffuse through it, and so the transmission of an action
potential along the axon happens in a `jumping action'. The areas between the myelination, called nodes of Ranvier, will
receive the influx of sodium ions as per usual, but the…

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