These nerves are actually single cells which have the function of carrying information from one area of the body to another area. Most of these cells are grouped together like the strands of a rope. Nerve cells have the same basic structure as all the other body cells, with a surrounding membrane containing the nucleus and cytoplasm, but they have a very special, elongated shape. A typical motor nerve, carrying instructions from the brain to the muscle, has a tuft of short, rootlike projections, called dendrites, at one end. At the other end is a long, thin projection, called the axon, which may split and divide up to 150 times and be attached to numerous muscle fibers.
Nerve cells can be thinner than the hairs on the head, but they can also be very long.
The average nerve running from the base of the spine to the tip of a toe is about three feet long, but many other axons are only a fraction of an inch in length. Most nerves act as links in a chain of nerve cells rather than connecting directly to a muscle. In such a chain, each axon is in near contact with the dendrites of the next cell, but there is a tiny gap between them. Nerve impulses jump this gap with the help of chemical messengers known as neurotransmitters.