PHYS20008 Lecture Notes - Lecture 5: Depolarization, Myelin
21 Jun 2018
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Lecture 5: Action Potentials II
Side note:
As a side note, inhibitors applied to the Na+/K+ pump (sometimes also written as Na+-K+-
ATPase) does not have an effect on action potential. Remember that action potentials are
triggered by the Na+/K+ voltage gated channels.
Therefore, action potentials can function normally with an Na+/K+ pump inhibitor present.
*Also remember that Na+/K+ voltage-gated channels is the passive movement of ions across
the membrane, Na+/K+ pump is active and therefore the ions involved will only be the ones
on the membrane.
Movement of action potentials:
We know that action potentials are fired frequently and not just once. On a single neuron,
these signals are fired along the axon- waves of depolarisation making its way down to the
axon terminals.
Na+ moves down the axon triggering a subsequent channel to open and allow Na+ to
come inside the cell and this process repeats again. While this is happening, the
receding gates begin to close and repolarise
*Note: We don’t lose amplitude of action potential as it moves down the axon.
In a single action potential, there are essentially three stages:
The first stage is where Na+ channels open and membrane potential depolarises to
threshold. This is called the graded potential.
Once at threshold, the action potential enters the absolute refractory period (which
doesn’t end until the ‘offshoot’ happens).
oThis period is ‘absolute’ because the neuron cannot fire another action
potential (they can’t ‘stack’ action potentials). This is because it is too busy
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Document Summary
As a side note, inhibitors applied to the na+/k+ pump (sometimes also written as na+-k+- Atpase) does not have an effect on action potential. Remember that action potentials are triggered by the na+/k+ voltage gated channels. Therefore, action potentials can function normally with an na+/k+ pump inhibitor present. *also remember that na+/k+ voltage-gated channels is the passive movement of ions across the membrane, na+/k+ pump is active and therefore the ions involved will only be the ones on the membrane. We know that action potentials are fired frequently and not just once. On a single neuron, these signals are fired along the axon- waves of depolarisation making its way down to the axon terminals. Na+ moves down the axon triggering a subsequent channel to open and allow na+ to come inside the cell and this process repeats again. While this is happening, the receding gates begin to close and repolarise.
