Nerves of the Arm

Three main nerves run past the elbow and wrist to the hand.

• Median nerve. This nerve passes down the inside of the arm and crosses the front of the elbow. At the wrist it goes through a "tunnel"-called the carpal tunnel-made up of the wrist bones and a tough band of connective tissue (ligament). The median nerve supplies muscles that help bend the wrist and fingers. It is a main nerve for the muscles that bend the thumb. The median nerve also gives feeling to the skin on much of the hand around the palm, the thumb, and the index and middle fingers. When the median nerve is compressed over a long period, it can cause carpal tunnel syndrome.
• Ulnar nerve. This nerve passes down the inside of the arm. It then passes behind the elbow, where it lies in a groove between two bony points on the back and inner side of the elbow. The ulnar nerve supplies muscles that help bend the wrist and fingers, and that help move the fingers from side to side. It also gives feeling to the skin of the outer part of the hand, including the little finger and the outer half of the back of the hand, palm, and ring finger. When the elbow is bumped over the ulnar nerve, it's often called hitting the "funny bone."
• Radial nerve. This nerve passes down the back and outside of the upper arm. The radial nerve supplies muscles that straighten the elbow, and lift and straighten the wrist, thumb, and fingers. The radial nerve gives feeling to the skin on the outside of the thumb and on the back of the hand and the index finger, middle finger, and half of the ring finger.