Now let’s look at the median nerve. Let’s go back to the elbow, where we saw it in the last section.
Here’s the median nerve, next to the brachial artery. To see where it’s going we’ll retract flexor carpi radialis. The median nerve first dives between the two heads of pronator teres. It then immediately passes between the two heads of flexor digitorum superficialis.
The median nerve (here it is) passes down the forearm between flexor digitorum superficialis and profundus. It emerges at the wrist to the radial side of the superficialis tendons. It's crossed by the tendons of palmaris longus and flexor carpi radialis.
The median nerve passes through the carpal tunnel to reach the hand. It lies just beneath the palmar aponeurosis, which has been removed here. The median nerve gives off this small motor branch to the thenar muscles, and then gives off these three common digital nerves. The common digital nerves break up into palmar digital nerves, two each for the thumb, index, and middle fingers, and usually one for the radial side of the ring finger.
The median nerve typically provides sensation to the medial half of the palm, the flexor aspect of the thumb, the index and middle fingers, and the radial side of the ring finger.
Of the extrinsic hand muscles, the median nerve supplies flexor digitorum superficialis, flexor pollicis longus, and the radial half of flexor digitorum profundus. Of the intrinsic hand muscles, it supplies only the three thenar muscles, and the radial two lumbricals.
Lastly, let’s look at the ulnar nerve. As you’ll recall from the last section, the ulnar nerve enters the forearm by passing round the medial epicondyle, and between the two heads of flexor carpi ulnaris.
Here’s the ulnar nerve. It runs down the forearm between flexor carpi ulnaris, and flexor digitorum superficialis, with profundus deep to it. Here, it gives off a dorsal sensory branch, which goes to the back of the hand. At the wrist, it runs along the radial side of flexor carpi ulnaris. Along with the ulnar artery it passes through the side tunnel in the edge of the flexor retinaculum.
Here it is emerging from the tunnel. Again the palmar aponeurosis has been removed. The ulnar nerve divides into a superficial branch and a deep branch. The superficial branch divides into palmar digital nerves for the little finger, and typically the ulnar side of the ring finger. The deep branch passes between the hypothenar muscles. To follow it we’ll remove the flexor tendons. The deep branch of the ulnar nerve runs across the palm in front of the interossei. It passes in between the two heads of adductor pollicis, we’ll remove the transverse head, to reach the most radial of the interossei.
The ulnar nerve typically provides sensation to the ulnar half of the back and the front of the hand, and to the little finger and the ulnar half of the ring finger.
Of the extrinsic hand muscles, the ulnar nerve supplies only the ulnar half of flexor digitorum profundus. Of the intrinsic hand muscles it supplies the hypothenar muscles, all the interossei, adductor pollicis and the ulnar two lumbricals.