Final answer:
The Long Thoracic Nerve originates from the roots of C5, C6, and C7 and is not a supraclavicular branch but part of the brachial plexus, specifically innervating the serratus anterior muscle for scapular motion.
Step-by-step explanation:
The Long Thoracic Nerve is not one of the supraclavicular branches of the brachial plexus; instead, it originates from the roots of C5, C6, and C7 which are part of the brachial plexus. Its main function is to innervate the serratus anterior muscle which plays a critical role in the movement of the scapula, including its ability to protract and upwardly rotate, essential for elevating the arm above the head.
The supraclavicular branches actually include nerves such as the dorsal scapular nerve, the nerve to subclavius, and the suprascapular nerve. These branches mainly supply the muscles and skin near the clavicle and shoulder. It is a common misconception that the long thoracic nerve is a supraclavicular branch due to its proximity to the brachial plexus and its origins from the cervical roots.