The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-C8, T1). It proceeds through the neck, the axilla (armpit region), and into the arm. It is a bunch of nerves passing through the cervico-axillary canal to reach axilla and supplies brachium, antebrachium and hand.
Read more about Brachial Plexus: Function, Additional Images