What are Na+ and Ca2+ Channels?
Sodium and calcium ion channels are two types of voltage dependent ion channels. These channels open or close not due to neurotransmitters, but instead due to voltage differences between the inside and outside of the cell. Voltage dependent sodium channels are typically involved in the action potential – a domino-effect propagation of nerve impulses along the axon. The sodium channel opens when the voltage reaches a certain activation threshold; the resulting influx of sodium then further activates the neuron (leading to more sodium channels opening). Eventually a second part of the sodium channel closes (otherwise they would keep themselves open forever). Incidentally, voltage dependent potassium channels are involved in bringing the neuron back to its resting state. Voltage dependent calcium channels are similar to voltage dependent sodium channels, and typically open on activation voltages. Their effect, however, is to cause calcium to enter the cell; the calcium then acts as a mess
