Brachial plexus

The brachial plexus is a network of nerves, running from the spine, formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5–C8, T1). The brachial plexus passes through the cervicoaxillary canal in the neck, over the first rib, and into the axilla (armpit region), where it innervates the upper limbs and some neck and shoulder muscles.

Structure

The brachial plexus is divided into five roots, three trunks, six divisions, three cords, and five branches. There are five "terminal" branches and numerous other "pre-terminal" or "collateral" branches that leave the plexus at various points along its length. A common structure used to identify part of the brachial plexus in cadaver dissections is the M or W shape made by the musculocutaneous nerve, lateral cord, median nerve, medial cord, and ulnar nerve.

Roots

The five roots are the five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck. The brachial plexus emerges at five different levels; C5, C6, C7, C8, and T1. C5 and C6 merge to establish the upper trunk, C7 continuously forms the middle trunk, and C8 and T1 merge to establish the lower trunk. Prefixed or postfixed formations in some cases involve C4 or T2, respectively. The dorsal scapular nerve comes from level C5 and innervates the rhomboid muscles which retract the scapula. The subclavian nerve originates in both C5 and C6 and innervates the subclavius, a muscle that involves lifting the first ribs during respiration. The long thoracic arise from C5, C6, and C7. This nerve innervates the serratus anterior, which draws the scapula laterally and is the prime mover in all forward-reaching and pushing actions.