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.