Ulnar nerve

One of the principal nerves of the arm. The ulnar nerve, a branch of the brachial plexus, runs down the full length of the arm and into the hand. The ulnar nerve controls muscles that move the thumb and fingers. It also conveys sensation from the 5th finger, part of the 4th finger, and the palm. A blow to the olecranon process, over which the ulnar nerve passes, causes a pins-and-needles sensation and pain in the forearm and 4th and 5th fingers. Persistent numbness and weakness in areas controlled by the ulnar nerve may be caused by an abnormal bony outgrowth from the humerus. This may be due to osteoarthritis or a fracture of the humerus, and surgery is needed to relieve the pressure on the nerve. Permanent damage to the ulnar nerve can result in claw-hand.


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