When the neurotransmitter falls off the channel closes and stops the signal. There are also voltage gated ion channels where there is no neurotransmitter receptor site, but the proteins are sensitive to changes in the voltage. Cells are positively charged on the outside and negatively charged on the inside. There are different types of channels, some allow potassium to flow through, some allow calcium to flow through, and some allow sodium to flow through. They are important for the basic activity and function of the nerves.
Nerve impulses follow along the nerve fibers carried by voltage gated sodium channels.
The ion channel conducts nerve impulse by separation of ions. We have many types of ions in our cells and the main ones that deal with all of the electrical things are sodium, potassium, and calcium. This allows the sodium ions to rush in and this rush of sodium ions changes the voltage next door in the sodium channels that haven't opened yet. When this voltage occurs, they open and new sodium ions flow in. This becomes a domino effect in which consecutive unopen sodium channels are opened by the entry of new sodium ions that cause the conduction of the impulse down the nerve fiber.