From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

Carpal tunnel syndrome occurs when a nerve is pinched in the wrist. This nerve, called the median nerve, is the connection from the brain and spinal cord, down to the finger tips. In patients with carpal tunnel syndrome, the median nerve is pinched as it passes through the wrist. Because of the compression, the nerve does not function properly.

How does the median nerve normally work?
Nerves are structures that relay messages to and from your brain. The nerve sends a message to your muscles when you want to move, and the nerve relays messages to your brain about sensations. Nerves control specific muscles, and nerves provide sensations for your body. The median nerve (the nerve that is affected in carpal tunnel syndrome) supplies messages to specific muscles of the hand. The median nerve also sends sensory information from most of the palm side of your hand and the thumb, forefinger, middle finger, and part of the ring finger.

The median nerve travels from branches off the spinal cord, down the arm, and into the wrist and hand. In the wrist, the median nerve passes through the carpal tunnel. Carpal comes from the Greek word for 'wrist'-that's what gives the tunnel its name. The carpal tunnel is actually made up of the wrist bones on the bottom, and a tight ligament on the top. The ligament that makes up the top of the carpal tunnel is not flexible, nor are the wrist bones. Coursing through the carpal tunnel is the median nerve, as well as tendons that attach to your fingers.

What is carpal tunnel syndrome?
Carpal tunnel syndrome is caused when there is pressure in the carpal tunnel that compresses the median nerve, causing the nerve to function improperly. Because the carpal tunnel is surrounded by bone on one side, and an inflexible ligament on the other, if pressure builds, the nerve has nowhere to go. Simply put, in carpal tunnel syndrome the nerve gets squished.

When carpal tunnel syndrome occurs, the median nerve is pinched, and the normal functions (as described above) are impaired. Problems that can occur in carpal tunnel syndrome include:

• Pain
• Numbness
• Tingling
• Weakness