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The Nerves

By

The Manual's Editorial Staff

Last full review/revision Jun 2020| Content last modified Jun 2020
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What are nerves?

A nerve is a bundle of nerve fibers from many nerve cells. The fibers are bundled together for strength and protection from injury.

  • Your nerves are like signal wires

  • Nerves send messages back and forth between your brain or spinal cord and your body

  • The messages from the brain tell your body what to do

  • Messages from the body let your brain know what is happening in your body

  • When nerves to part of your body are injured or don't work you may not be able to move or feel that part of your body

How do nerves work?

There are billions and billions of nerve cells in your brain, your spinal cord, and in clumps just outside your spinal cord.

Each nerve cell has a microscopic body:

  • The body of the nerve cell is responsible for processing nutrients and keeping the cell alive

Each nerve cell has fibers going to and from it:

  • Input fibers receive signals from other nerve cells or from receptors in your sense organs

  • Output fibers send signals to other nerves, to muscles, or to other organs

  • Signals travel only one way in a nerve cell

Sometimes nerve fibers are dozens of centimeters long. For example, a single nerve fiber may run from near your spinal cord all the way to your toe. Some nerve fibers that go to your skin or your organs have sensory receptors. For example, the receptors at the end of nerve fibers in your skin detect things that are sharp or hot.

Because each individual nerve fiber is very tiny, the fibers are bundled together for strength. Large fibers leave your spinal cord and split like the branches of a tree to go all the different parts of your body. Different nerves carry signals to and from a specific part of your body.

Although nerve fibers and their signals act a lot like a wire carrying electrical signals, that's not exactly right. Nerve cells really send their signals using chemicals.

  • Chemical changes take place progressively along the length of a nerve fiber

  • Those changes are quick but not nearly as fast as electricity

  • When the chemical changes reach the end of the nerve fiber, they release other chemicals called neurotransmitters

  • The neurotransmitters drift across a microscopic gap where they hit the chemical receptors of another cell

  • The neurotransmitters trigger chemical changes in that other cell

  • If that cell is a nerve cell, then the progressive chemical changes continue down the fibers of that cell to pass the signal along

To help the chemical signals travel quickly, nerve fibers are wrapped in a fatty layer called a myelin sheath. If the myelin sheath is damaged, messages either aren't passed or are passed more slowly along nerves.

Insulating a Nerve Fiber

Most nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation around an electrical wire, the myelin sheath enables electrical impulses to be conducted along the nerve fiber rapidly.

When the myelin sheath is damaged, nerves do not conduct electrical impulses normally.

Insulating a Nerve Fiber

What can go wrong with nerves?

Many problems can affect the nerves:

Once nerve cells die, they can't grow back. However, if the body of the nerve cell isn't hurt, nerve fibers sometimes grow back slowly. Doctors sometimes can sew cut nerves back together and get them to work. Damage to the myelin sheath is usually permanent.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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