Brachial Plexus

The three main nerves of the brachial plexus are as follows.
The radial nerve. This runs round the back of the arm and down the outside of the forearm. It supplies the extensor muscles of the elbow, wrist and hand.
The ulnar and median nerves. These run down the inside and middle of the limbs respectively and supply the forearm muscles of the wrist and hand. The ulnar nerve crosses in the groove between the back surface of the internal epicondyle of the humerus and the olecranon process.
The thoracic nerves. These supply the muscles of the chest and the main part of the