What is the Brachial Plexus?

    The brachial plexus is a complex network of nerves arising from the spinal cord at the level of the neck and supplying all the muscles of the upper extremity. In this article, we'll describe the origin of the plexus, its course from the neck and its distribution.

The Origin

    The brachial plexus originates from 5 nerve roots - the 5th cervical nerve root, the 6th cervical nerve root, the 7th cervical nerve root, the 8th cervical nerve root and the 1st thoracic nerve root. Each nerve root is derived from the corresponding ventral or primary rami of the spinal nerve. The nerve roots unite to become 3 trunks. The 5th and 6th cervical nerve roots unite to form the upper trunk, the 8th cervical and 1st thoracic nerve roots unite to form the lower trunk while the 7th cervical nerve root continues as the middle trunk.

    Each trunk then splits to form 2 divisions - an anterior and a posterior division; therefore, the 3 trunks give rise to 6 divisions (3 anterior divisions and 3 posterior divisions). The anterior divisions of the upper and middle trunk unite to form the lateral cord; the anterior division of the lower trunk continues as the medial cord and all 3 posterior divisions unite forming the posterior cord. The nerve cords derive their names with respect to their relationship with the axillary artery. The lateral cord lies on the lateral (or outer) side of the axillary artery; the medial cord lies on the medial (or inner) side of the axillary artery and the posterior cord lies behind the axillary artery.

    The cords then branch out forming different nerves that supply all of the muscles of the upper extremity.

Nerve Branches of the Plexus

    Branches of the Nerve Roots

        • Dorsal scapula nerve - This nerve is a branch of the 5th cervical nerve root. It innervates the rhomboid minor and major muscles as well as the levator scapulae muscles
        • Long thoracic nerve - Its branches come from the 5th, 6th and 7th cervical nerve roots and unite to form the long thoracic nerve. This nerve supplies the serratus anterior muscle

    Branches of the Trunks

        • Nerve to subclavius - This nerve is a branch of the upper trunk (derived from the 5th and 6th cervical nerve roots). It innervates the subclavius muscle
        • Suprascapular nerve - The suprascapular nerve is also a branch of the upper trunk of the plexus. It supplies the supraspinatus and infraspinatus muscles

    Branches of the Lateral Cord

        • Lateral Pectoral Nerve - This nerve supplies the pectoralis major muscle
        • Musculocutaneous Nerve - which innervates the coracobrachialis, the brachialis and the biceps brachii muscles. The nerve continues as the lateral cutaneous nerve of the forearm which supplies the lateral side of the skin of the forearm
        • Lateral root of the Median Nerve

    Branches of the Medial Cord

        • Medial root of the Median Nerve - The lateral root and medial root of the median nerve unite to form the median nerve. This nerve supplies all of the muscles on the anterior forearm and hand not supplied by the ulna and radial nerves
        • Medial cutaneous Nerve of the Arm - innervates the anterior and medial aspect of the skin of the arm
        • Medial cutaneous Nerve of the forearm - supplies the medial side of the skin of the forearm
        • Ulna nerve - supplies the flexor carpi ulnaris, the medial side of flexor digitorum profundus and most of the small muscles of the hand. The ulna nerve supplies the medial side of the hand and the medial one and a half fingers on the palmar side and the medial two and a half fingers on the dorsal side

    Branches of the Posterior Cord

        • Upper Subscapular Nerve - supplies the upper side of the subscapularis muscle
        • Thoracodorsal Nerve - supplies the latissimus dorsi muscle
        • Lower Subscapular Nerve - supplies the lower side of the subscapularis muscle together with the teres major muscle
        • Axillary Nerve - its anterior branch supplies the deltoid muscle while its posterior branch supplies the teres minor muscle
        • Radial Nerve - the radial nerve supplies the triceps brachii, the supinator, the anconeus, the extensor muscles of the forearm and brachioradialis. The radial nerve also innervates the skin of the posterior arm as the posterior cutaneous nerve of the arm.

Figure: A representation of the brachial plexus.

diagramatic brachial plexus nerve network


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