Biology - Transmission of Nerve Impulses (action potential)
Transmission of Nerve Impulses (action potential)
Nerve cells are electrically excitable; meaning that when they are
stimulated, they can produce electrical impulses which travel along the
nerve fibre. This is possible because an action potential or voltage is
created across the nerve cell membrane due to the distribution of Na+ and
K+ ions either side of the membrane - that is, inside and outside the axon.
_Resting neuron_ - one which is not transmitting an impulse; the inside
of the cell is negatively charged compared with the outside; the cell
membrane is electrically polarised.
_Stimulated neuron_ - one along which an electrical impulse travels
* in moments (milliseconds), the cell membrane becomes _depolarised_ at
the point along the axon where there is a gap in the myelin sheath (node of
Ranvier); positive Na+ ions enter through channels and the inside becomes
* this is followed by the exit of K+ ions which causes_ repolarisation_
restoring the resting potential
A wave of _depolarisation_ moves along the axon from node to node as there
is exchange of Na+ and K+ ions.
An impulse which moves along an axon in this way is called an _action
potential_. It is rather like a domino effect.
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