The medial cord gives off 3 non-terminal branches: the medial pectoral, medial brachial cutaneous, and medial antebrachial cutaneous nerves. The lateral cord gives rise to a single nonterminal branch, the lateral pectoral nerve, that contains the spinal levels of C5 to C7 and innervates the pectoralis major muscle. Cords continue as 5 terminal branches while giving off seven other nerves ranging in function. The majority of the branches of the brachial plexus arise from cords. There are no branches from any division within the brachial plexus. The suprascapular nerve travels through the scapular notch to provide innervation to the supraspinatus and infraspinatus muscles. The suprascapular nerve and nerve to the subclavius originate from the superior trunk and contain the spinal levels of C5 and C6. Two nerves typically branch from the superior trunk while the inferior and middle trunks are devoid of branches. There is also a contribution from the C5 root to the phrenic nerve. The dorsal scapular nerve innervates the levator scapulae muscle, rhomboid major and minor muscles and may travel with the dorsal scapular artery if it is present. The long thoracic nerve innervates the serratus anterior muscle and travels with the lateral thoracic artery. Both nerves are often observed piercing the middle scalene muscle. The dorsal scapular nerve originates from the rami of C5, while the long thoracic nerve originates from the rami of C5, C6, and C7.
Two nerves originate completely from the roots of the brachial plexus: the dorsal scapular nerve and long thoracic nerve. The branches, terminal and otherwise, of the brachial plexus are expanded on below in the section Nerves and Muscles. The final subdivision of the brachial plexus consists of five terminal branches containing different contributions from the C5-T1 spinal levels. The result of this “mixing” of nerve fibers is that the lateral cord contains components of C5, C6, and C7, the medial cord with contribution from C8 and T1, and the posterior cord carrying fibers from all levels of the brachial plexus (C5 to T1). The 3 posterior divisions converge to form the posterior cord while the anterior division from the superior trunk and the anterior division from the middle trunk join to form the lateral cord. The medial cord is formed as a continuation of the anterior division from the inferior trunk. The 3 cords (posterior, medial, and lateral) are formed from the anterior and posterior divisions, and they are named based on their relationship to the 2 parts of the axillary artery. Each of the trunks of the brachial plexus continues as an anterior and posterior division to form lateral, posterior, and medial cords. The 3 trunks continue from the posterior triangle into the axilla with C5 and C6 roots forming the superior trunk, C8 and T1 roots forming the inferior trunk, and the C7 root continuing as the middle trunk.Ĭontinuing from the trunks are bundles that are called divisions. Ventral rami from spinal nerves C5 through T1, often referred to as roots of the brachial plexus, come together to allow their fibers to intermingle forming superior, inferior, and middle trunks. As the brachial plexus travels through the posterior triangle of the neck into the axilla, arm, forearm, and hand, it contains various named regions based on how the plexus is formed. The brachial plexus provides somatic motor and sensory innervation to the upper extremity, including the scapular region.