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Resting potentials and action potentials
Neurones have very specialised membranes filled with many channel proteins that are
specific either to sodium or potassium ions.
Sodium-potassium pumps actively transports sodium ions out of the cell and potassium ions
into the cell.
There are also voltage-gated channels which are specific to ions:…

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7. Potassium ions diffuse out of the cell bringing the potential difference back to negative
inside the cell. This is called repolarisation.
8. The outflow of potassium ions overshoots the potential difference to just below -70mV,
which overcompensates the change in electronegativity ­ this is called hyperpolarisation ­
and then…

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Transmission of an action potential
When an action potential arrives sodium channels open, which causes an influx of sodium
ions into the cell, depolarising that section of the membrane.
This disrupts the balance of ions in surrounding areas so that local currents are created in
the cytoplasm, causing sodium channels…

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Sodium and potassium ions cannot diffuse through this fatty area.
The ionic movements that create an action potential cannot occur over much of the
length of the neurone.
The gaps between the Schwann cells are called nodes of Ranvier.
The ionic changes that cause an action potential only occur at…

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Damilola Fasoyiro A2 Biology


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