There are seven main nerves that innervate the muscles and skin of the human arm. They all arise from the brachial plexus.
1) Median nerve. It is formed by the medial and lateral roots that arise from the medial and lateral cords of terminal the brachial plexus. It supplies sensitive and motor branches to the skin and muscles that control the fingers and hand movements.
2) Radial nerve. It originates directly from the brachial plexus posterior cord, dividing into two terminal branches. It innervate the muscles of the arm and forearm.
3) Ulnar nerve. Arising from the brachial plexus medial cord, it supplies inner muscles and skin of the hand
4) Axillary nerve. It projects from the posterior cord of the brachial plexus, containing nerve fibers from cervical roots C5 and C6. It supplies the shoulder muscles.
5) Musculocutaneous nerve: It is formed from fibers that comes off the lateral cord of the same plexus. It gives off different smaller branches that supplies the biceps and brachialis muscles, the humerus, and forearm skin.
6) Medial cutaneous nerve of the forearm. It comes off the medial cord of the brachial plexus.
7) Medial cutaneous nerve of the arm. It also arises from the medial cord.