Voltage-gated ion channels

Voltage-gated ion channels are present within in all electrically excitable cells. Their role within the plasma membrane is to generate an action potential. 

The opening of these channels is dependent on the strength of a stimulus, which causes depolarisation of the plasma membrane. For example, with cells containing voltage-gated Na+ channels, the stimulus causes the opening of these said channels allowing the movement of the Na⁺ across the plasma membrane, down an electrochemical gradient.