Anatomy, Shoulder and Upper Limb, Axillary Nerve

The brachial plexus is the network of innervation to the upper limb. It originates in the neck and passes between the anterior and middle scalene muscles. It courses beneath the transverse cervical artery in the posterior triangle of the neck and continues underneath the clavicle and first rib. Finally, it travels toward the axilla where the terminal branches arise to provide motor and sensory innervation to the upper limb. The brachial plexus is comprised of ventral rami of C5 down to T1, providing nervous stimulation for muscular actions including flexion, extension, pronation, supination, abduction, adduction, external and internal rotation at the shoulder, arm, forearm, and hand. It also provides sensory innervation to the upper limb. This nerve network begins as roots then continue to divide into trunks, divisions, cords, and lastly terminal branches. The 5 terminal branches are the musculoskeletal nerve, median nerve, ulnar nerve, radial nerve, and the axillary nerve. Each terminal branch has an area where it provides motor and sensory innervation in the upper limb. The regional orientation of each branch assists with understanding the actions which take place secondary to stimulation of specific muscles. When the body is in the anatomical position, the muscles of the arm and forearm which face anteriorly are mostly flexors, as opposed to muscles that are positioned posteriorly, which are primarily extensors. Muscles that cross joints and positions from anterior to posterior or posterior to anterior will participate in pronation or supination, respectively. The axillary nerve is the terminal branch and will be our area of focus to be discussed in this article.
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