The nerves of the hand are those vessels of the nervous system that innervate the hands and fingers. These vessels, which branch off in the hand into smaller nerves upon crossing the wrist, come from three major nerves that run all the way down the arm: the radial, median, and ulnar nerves. Carrying signals known as afferent or efferent that run toward the central nervous system or away from it, respectively, the nerves of the hand convey information to and from the brain. Information traveling from the brain to the hand includes motor signals, which tell the muscles there to move the hand and fingers. Conversely, that traveling from the hand to the brain includes sensory signals, which send the brain messages about touch, such as whether an object feels soft or sharp, and about pain.
Originating from nerve roots exiting the spinal cord at the height of the four lower cervical vertebrae and topmost thoracic vertebra in the neck, the radial, median, and ulnar nerves of the hand all begin just above the shoulder and course down the arm. The radial nerve travels down the same side of the arm as the radius bone in the forearm, which is the thumb side of the arm. Likewise, the ulnar nerve is found to the side of the ulna bone in the forearm, or the pinky side. The median nerve, as its name suggests, runs down the middle of the arm, entering the hand through the carpal tunnel in the center of the wrist.
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The radial nerve, after serving many of the muscles found on the back of the arm, is a superficial nerve once it reaches the forearm, meaning that it lies close to the skin. Its superficial branch supplies much of the dorsal surface of the hand, namely the skin and its sensory receptors. Branches of this nerve innervate both sides of the back of the index finger, the radial side of the back of the ring finger, both sides of the back of the middle finger, and the radial and ulnar sides of the back of the thumb.
Next to the radial nerve is the median nerve, the middle of the three major nerves of the hand. It runs directly down the center of the forearm and enters the hand via the carpal tunnel, a passage between the cluster of carpal bones just beyond the wrist joint. This nerve also supplies the skin of the first three fingers on the palm side of the hand, as well as the lumbrical muscles on the radial side of the hand, deep muscles between the bones within the palm that assist in flexing and extending the fingers.
The third of the major nerves of the hand is the ulnar nerve. It comes into the hand along the palm side and is more superficial than the median nerve, though once in the hand it divides into superficial and deep branches. The superficial branch innervates the palmaris brevis muscle as well the skin on the ulnar portion of the hand. It also supplies the skin on the palm surface of both sides of the pinky finger and the ulnar side of the ring finger. Beneath this, the deep branch of the ulnar nerve supplies many of the muscles of the hand, including those that spread and bring together the fingers and those that perform opposition, the act of bringing the thumb inward to touch the tips of the four fingers.