Anatomy

Brachial Plexus Anatomy

The brachial plexus is a network of nerves starting from five nerve roots in the upper spine and ending in the five main nerves that control movement and sensation in the arm. It is located near where the neck joins the shoulder, behind the clavicle and between the spine and the upper arm, just distal to the axilla.

The nerves from the spine join and split in a pattern that forms five sections of the brachial plexus: roots, trunks, divisions, cords, and nerves. The anterior branches join to form upper (C5 and C6), middle (C7), and lower (C8 and T1) trunks. Each trunk separates into anterior and posterior divisions behind the clavicle. These combine to form three cords, lateral, medial, and posterior, which are named according to their position relative to the axillary artery.

These three cords then divide and recombine to form the major nerves of the arm. The posterior cord divides into the axillary and radial nerves. The medial cord divides into the ulnar nerve and one limb of the median nerve. The lateral cord divides into the musculocutaneous nerve and one limb of the median nerve.

Microscopic Anatomy

This figure illustrates the complex nerve pathways within the brachial plexus. Many small nerves branch off from the brachial plexus. As a result, each of the major nerves of the arm receives input from multiple spinal levels, and each spinal root innervates multiple nerves. Thus, the loss of a portion of nerve fibers at one level can be compensated for by nerve fibers at another level. However, because of the complexity of the nerve pathways within the brachial plexus, surgical repair cannot restore the normal anatomy.