Brain Primer

Ion Channels and Action Potentials

  • Published14 Nov 2022
  • Author Diane A. Kelly
  • Source BrainFacts/SfN
animated image of an ion
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Ions are electrically charged atoms that can only cross a neuron’s cell membrane through tunnel-like proteins called ion channels. These tunnel-like proteins act like gates, allowing some ions to enter or leave the cell, but keeping others out. Ions that enter or leave the cell change the voltage difference across the membrane. This change in voltage influences the neuron’s likelihood of generating an electrical signal.

In mammals, the voltage difference across the membrane of a resting neuron is around -70 millivolts (mV), more negative inside the cell than on its outer surface. That membrane potential is affected by signals arriving from other neurons in its circuit, which can make the membrane potential less negative (depolarized) or more negative (hyperpolarized) by opening ion channels in the dendrites. If the sum of all the signals at the dendrites rises to match the membrane’s threshold voltage, a series of voltage-sensitive ion channels opens automatically, triggering an electrical impulse called an action potential, which moves down the axon towards the next neuron in the circuit.


Adapted from the 8th edition of Brain Facts by Diane A. Kelly.

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