<prompt> A 29-year-old man comes in with a stab wound, cannot raise his arm above horizontal, and exhibits a condition known as winged scapula. Which of the following structures of the brachial plexus would most likely be damaged?Medial cordPosterior cordLower trunkRoots  <response>: Winged scapula is caused by paralysis of the serratus anterior muscle that results from damage to the long thoracic nerve, which arises from the roots of the brachial plexus C5-C7 