Nerve cells, or neurons, receive electrochemical signals, process them and transmit them to other cells. Most often, these are other neurons, but nerve cells signal muscle cells and other active cells of the body as well. Sensory nerve cells also react to their environments, sending signals to the central nervous system in response to changes.
Nerve cells have four basic parts. Each has a branching series of receivers, called dendrites, that detect incoming nerve impulses or other changes to the environment. The cell body contains the nucleus and processes the stimulus to send out its own signal. This signal is sent out along the axon, a long, sometimes very long, extension of the cell that acts as a wire for the signal. The axon ends with what is known as the terminal bundle, which interacts with the next nerve cell in the chain.
Nerve cells transmit signals via a chain reaction of electron action potentials. Certain charged particles move in and out of the axon in a rapid chain reaction. This action is very fast, although not as fast as a normal electrical current traveling through a metal wire. However, to transmit coherently over a long distance, the axons need to be insulated like a wire. Myelin sheaths, made of cholesterol-type compounds, serve this purpose.