The brachial plexus is made up of nerves from the lower cervical nerves C5-C8 and the first thoracic nerve. It supplies nerve fibers to the following areas: Chest, Shoulder, Arm, Forearm, Hand. The brachial plexus begins at the neck and crosses the upper chest to the armpit. Injuries to this network of nerves can occur when the arm is forcibly pulled or stretched.