What Are Nerves Like?

Nerves form part of the complex system in the human body known as the nervous system. The brain, the spinal cord and the individual nerves are all part of this system. Its function is to monitor changes in the human body, both those caused by external factors and also internal changes, and then bring about responses that help the body work at its best.

Individual nerves look like white tubes; the major nerves are quite thick and can be seen with the naked eye. Smaller nerves can only be seen with a microscope. All nerves are made up from nerve fibres and these consist of packages of nerve cells.

Nerve cells come in various shapes and sizes. Some, such as those in the nerves that lead from the spine to the hands and feet, can be very long. The ends of the nerve cells have lots of projections, so they can communicate with other nerve cells and cells such as muscle cells; the middle of the nerve cell, called the axon, is just a long thin tiny tube.

The cells whose job it is to keep our body informed of conditions in the outer world are the nerve cells.
In lower forms of life, nerve cells are located in the skin and they directly transmit messages to the deeper parts of the body. But in human beings and other complex organisms, most of the nerve cells are actually in the body, though they may pick up their "messages" in the skin by means of delicate "antennae".
The purpose of the nerve cells is to transmit messages throughout the body, each message to the proper place. The nerve fibres along which these messages go are constructed like a cable, and are amazingly efficient.
Actually there are four chief types of nerve cells, or "nerves"," or nerve units. These are the completely independent units of nerve cells in the body, each organized to do its special job. One type receives messages such as heat, cold, light, and pain from the outer world, and conducts them to the interior of the body. These might be called "the sensory units".
Another type might be called "the motor unit". It receives impulses from the sensory units and responds to them by sending a nerve current to various structures in the body, such as the muscles and the glands. The reaction that results is called a "reflex", A "heat message", for example, would make certain muscles react and pull a hand away from a hot surface.
A third type of nerve unit does a connecting job. It transmits messages over longer distances in the body. It connects motor cells in one part of the body with sensory cells in another part.
A fourth type of nerve unit has the job of carrying messages from the outer world, such as cold, heat, and pain, to the brain where we "translate" the message into feeling.

Nerves are bundles of nerve fibers enclosed in the sheath of connective tissue.