Voltage-gated ion channels are a class of transmembrane proteins that open and close in response to changes in the membrane potential — the voltage difference across a membrane. These channels have a voltage-sensor domain that moves under the influence of the charge and a highly selective gated transmembrane channel for the ions' movement. On receiving an impulse, the cell membrane depolarizes, becoming more positive. This voltage difference shifts the voltage sensors upwards, opening the gated channel, which allows ions to move down their concentration gradient. Depending on the ion-specificity, there are four types of voltage-gated ion channels. Voltage-gated sodium channels, abundantly found in the neurons, aid in the rapid influx of sodium ions, causing membrane depolarization. Voltage-gated potassium channels, found in diverse cell and tissue types, allow rapid efflux of potassium ions, restoring the membrane potential. Voltage-gated calcium channels allow the influx of calcium ions that trigger neurotransmitters' release into the synapse. Lastly, the voltage-gated chloride channels permit chloride ions' influx and help regulate the cell volume. These are distributed in neurons, muscles, and kidneys.