Brachial plexus is divided into roots, trunks, divisions, cords and branches. The rami (divisions) of the spinal nerves from C5, C6, C7, C8, and T1, are referred to as the five roots of brachial plexus. They merge together in a certain order to form three trunks: C5 and C6 roots merge to form the superior or the upper trunk. C7 travels alone, and continues as the middle trunk. C8 and T1 roots join to form the inferior or lower trunk.