The upper limb is supplied by the radial nerve and includes all muscles, overlying skin and joints. It originates from the brachial plexus' posterior cord. The brachial plexus consists of the collection of nerve fibers that run starting from the spine, up through the neck and into the arm. The main radial nerve separates into the deep branch of radial nerve, which then extends into the superficial branch in the back of the hand. The radial nerve, along with its branches, supplies all of the dorsal muscles. The dorsal muscles include the triceps, the hand and wrist extensors and the most of the hand on the back side. The deep branch of radial nerve continues around the radius' lateral side on the back side of the forearm between the two fiber planes of the supinator muscle. This muscle is responsible for supination of the forearm. The deep branch of radial nerve then travels downward in between deep and superficial muscle layers and into the middle section of the forearm.