Sodium voltage-gated ion channels
Role in an Action Potential
The voltage gated sodium ion channels are responsible for the influx of sodium into a neurone causing depolarisation of the membrane and therefore an action potential. Voltage gated soium ion channels have three states:
Voltage-gated sodium ion channels open when a membrane is depolarised from its resting membrane potential (-70 mV). Depolarisation only occurs when the voltage across the plasma membrane increases above a certain threshold (-55 mV). When the membrane is fully depolarised, and the action potential is at its peak, the channels inactivate themselves by closing the inactivation gate. During inactivation the voltage gated sodium ion channel is unable to be stimulated by depolarisation of the membrane so an action potential cannot be created. When the voltage across the membrane reduces to a low enough value the inactivation gate opens and the activation gate closes so the channel is again able to be stimulated by depolarisation of the membrane.