Peripheral nerves are tubes that extend out of the spinal cord and transmit electrical impulses that provide sensory and motor information to various stimuli and muscles to allow us to feel and move our body. There are a variety of nerves in the upper extremities, mostly of which originate from our neck, or cervical spine.
- Brachial Plexus- a group of nerves that control the muscles and the sensation throughout the arms.
- There are various components of the brachial plexus including, roots, trunks, divisions, cords, and branches. An injury can occur at any of these components, causing various symptoms depending on the location.
- Injuries can range from mild stretch to complete tears at the roots, which results in an arm with no sensation or ability to move or function.
- Injuries often occur during accidents where the neck and arm move in opposite directions, as can occur in motor vehicle accidents or birth trauma.
- Radial Nerve- begins at the nerve roots C5, C6, C7, C8, and T1 in the brachial plexus. It wraps around the humerus and provides input to the triceps muscle, which extends the elbow. It travels around the outside of the elbow into the dorsal forearm and provides the input to the muscles that extend the wrist and fingers.
- This nerve provides the sensation to the back of the hand and thumb, except the small and ring fingers.
- Injuries can occur with injury to the humerus and from compression in the forearm, called “radial tunnel syndrome.” Injuries can cause weakness in the ability to extend the wrist and fingers to paralysis and the inability to extend the wrist and fingers, called wrist drop.
- Median Nerve- begins at the nerve roots C5, C6, C7, C8, and T1 in the brachial plexus. While this nerve travels along the inside of the upper arm, it does not provide any function or sensation until it crosses the elbow. In the forearm, it provides input to the muscles the flex the fingers and wrist and the muscles the pronate (palm down) the forearm. It also supplies the muscles in the thenar eminence (OP, FPB, and APB) and lumbricals 1 and 2. It does not supply the FCU or the FDP muscles of the small and ring fingers, which is supplied by the ulnar nerve.
- This nerve provides the sensation to the palm over the thenar muscles, the thumb, index, long, and half of the ring finger.
- Injuries can cause weakness in forearm pronation, wrist flexion, and finger flexion. There may also be thenar muscle atrophy and difficulty with opposition of the thumb. Finally, there may be altered sensation such as numbness, tingling, or pins and needles to palm over the thenars, thumb, index, long, and half of the ring finger.
- The median nerve further divides into the common palmar digital nerves. The first supplies lumbrical 2 and runs to the index and middle fingers where they divide into two to form the proper digital nerves on each side of the digit. The second goes to the middle and radial side of the ring fingers and divides into two to form the proper digital nerves on each side of the digit. It also communicates with a small branch of the ulnar nerve to lumbrical 3.
- Ulnar Nerve- begins at C8 and T1 nerve roots in the brachial plexus. It travels down the inside of the upper arm to the inside of the elbow. The “funny bone” feeling that travels down to the small and ring finger when you hit the inside of the elbow is actually the ulnar nerve. The inside of the elbow is a common point of compression, called cubital tunnel syndrome. It then continues to travel down the inside of the forearm into the side of the hand by the small finger. The ulnar nerve is responsible for providing input to the FDP muscles of the small and ring fingers (bends DIP joint of small and ring fingers), the FCU (flexes wrist and ulnarly deviates), hypothenar muscles, lumbricals 3 and 4, and the palmar and dorsal interossei.
- This nerve provides sensation to the small finger side of the palm, the small finger and half of the ring finger, and the back (dorsal) side of the small finger.
- Injuries can provide a variety of symptoms including altered sensations such as tingling, numbness, pins and needles to the small finger side of the palm, small finger, and half of the ring finger, weakness in many of the intrinsic muscles of the hand, causing decreased grip strength, and “clawing” of the small and ring fingers due to muscle imbalances.
- The ulnar nerve further divides into the common palmar digital nerves, which then further divides into proper digital nerves of the ulnar side of the ring finger and the small finger.
Some of the common conditions that impact the nerves of the hand include brachial plexus injuries, cubital tunnel syndrome, Guyon’s canal syndrome, carpal tunnel syndrome, radial tunnel syndrome, posterior interosseous nerve syndrome, and anterior interosseous nerve syndrome.