Shoulder & Brachial Plexus LO5

5. Diagram the brachial plexus beginning with nerve roots and ending with terminal branches. Label the nerve roots, trunks, divisions, cords, and the 5 main terminal nerves of the upper limb. Identify the major muscle groups innervated by these terminal nerves.

Most nerves of the upper limb arise from the brachial plexus, which is made up of the ventral primary rami of C5-T1 spinal nerves. These are the roots of the plexus. The roots unite to form three trunks (superior, middle, inferior), which divide into anterior and posterior divisions. The anterior divisions ultimately innervate anterior compartment muscles (flexors) and the posterior divisions ultimately innervate posterior compartment muscles (extensors). These divisions unite to form cords, which are named based on their location relative to the axillary artery: lateral, medial, and posterior cords. These cords give rise to branches or terminal nerves that innervate the upper limb.

Brachial plexus components (proximal-distal):

    • ROOTS
      • Ventral primary rami of C5-T1
    • TRUNKS
      • Superior (C5-C6)
      • Middle (C7)
      • Inferior (C8-T1)
      • Anterior (innervate anterior/flexor compartment muscles)
      • Posterior (innervate posterior/extensor compartment muscles)
    • CORDS (name based on location relative to axillary a.)
      • Medial (anterior division of inferior trunk; sometimes a branch of anterior division of middle trunk)
      • Posterior (all three posterior divisions)
      • Lateral (anterior divisions of superior & middle trunks)
      • Musculocutaneous n.
        • A terminal branch of lateral cord (C5-C7)
      • Axillary n.
        • Posterior cord (C5-C6)
      • Radial n.
        • Terminal branch of posterior cord (C5-T1)
      • Median n.
        • Contributions from lateral & medial cords (C6-T1)
      • Ulnar n.
        • Continuation of medial cord (C7-T1)

There are various, supraclavicular branches directly off the certain roots and trunks that should be noted, specifically:

    • Dorsal scapular n. (C5)
    • Long thoracic n. (C5-C7)
    • Suprascapular n. (Superior trunk)

You can follow the formation, distribution, and paths of nerve fibers as terminal nerves are formed from the brachial plexus in the images below. You should be able to draw a diagram of the brachial plexus and know the spinal cord levels of the terminal nerve branches: musculocutaneous, axillary, radial, median, & ulnar.