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Brachial plexus: Anatomy

  • The brachial plexus is formed by the union of the anterior primary divisions of the 5th-8th cervical nerves and the 1st thoracic nerve
  • As the nerve roots leave the intervertebral foramina they converge, successively forming trunks -> divisions -> cords -> branches -> terminal nerves
    • Mnemonic for order: Randy Travis Drinks Cold Beer (Roots > trunks > cords > branches)
  • Trunks:
    • 3 trunks: superior, middle, and inferior
    • Located between the anterior and middle scalene muscles
  • Divisions:
    • Formed as the trunks pass over the lateral border of the 1st rib and under the clavicle
    • Each of the 3 trunks divides into anterior and posterior divisions
  • Cords:
    • Formed as the brachial plexus emerges below the clavicle and the fibers of the divisions combine again to form 3 cords
    • Named according to their relationship to the axial artery: lateral, medial, and posterior
    • At the lateral border of the pectoralis minor muscle, each cord gives off a major branch before ending as a terminal nerve
  • Terminal Nerves
    • Lateral cord gives off the lateral branch of the median nerve and ends as the musculocutaneous nerve
    • Medial cord gives off the medial branch of the median nerve and ends as the ulnar nerve
    • Posterior cord gives of the axillary nerve and terminates as the radial nerve