Anatomy Review: The Brachial Plexus
The components of the Brachial Plexus is a topic that is always important to review, as it is so significant to everyday clinical practice. Here is a brief overview of the divisions and actions of each component.
Axillary Nerve – It supplies two muscles, deltoid (a muscle of the shoulder), and teres minor (one of the rotator cuff muscles). The axillary nerve also carries sensory information from the shoulder joint, as well as the skin covering the inferior region of the deltoid muscle – the “regimental badge” area (which is innervated by the Superior Lateral Cutaneous Nerve branch of the Axillary nerve). When the axillary nerve splits off from the posterior cord, the continuation of the cord is the radial nerve.
Radial Nerve – The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm, as well as the associated joints and overlying skin.
It originates from the posterior cord of the brachial plexus with roots from C5, C6, C7, C8 & T1. The radial nerve and its branches supply the dorsal muscles, such as triceps brachii, the extrinsic extensors of the wrist and hands, and the cutaneous nerve supply to most of the back of the hand. (The ulnar nerve cutaneously innervates the back of the little finger and adjacent half of the ring finger). The radial nerve divides into a deep branch (which becomes the posterior interosseous nerve), and continues as the superficial branch which goes on to innervate the dorsum (back) of the hand.
Musculocutaneous Nerve – A terminal branch of the lateral cord of the brachial plexus, containing fibers form the C5, C6, and C7 spinal segments. It pierces coracobrachialis, continuing downwards and laterally between biceps and brachialis muscles. At the elbow, it pierces the deep fascia to continue as the lateral cutaneous nerve of the forearm. It gives muscular branches to coracobrachialis, biceps, and brachialis, and an articular branch to the elbow joint.
Median Nerve – The median nerve (C5, 6, 7, 8, T1) is motor to most of the long flexors of the forearm and muscles of the thenar eminence. It supplies sensibility to the skin of the palm, (usually) radial three and half digits, elbow, wrist, and hand joints.
Ulnar Nerve – The ulnar nerve (C7, 8, T1) is the continuation of the medial cord of the brachial plexus. It is usually joined in the axilla by fibers from C7. The ulnar nerve is motor to most of the small muscles of the hand, to flexor carpi ulnaris, and to the ulnar half of flexor digitorum profundus. It provides sensibility to the ulnar aspect of the hand.
Dorsal Scapular Nerve – Arising from C5 ventral ramus (often with contributions from C4), the nerve pierces the scalenus medius to travel behind the levator scapulae (as it serves it with motor innervation) with the deep branch of the dorsal scapular artery. They travel to and supply the rhomboids major and minor.
Suprascapular Nerve – Arises from the upper trunk of the brachial plexus containing fibers from C5 and C6 spinal segments. It passes through the suprascapular foramen (located on the superior aspect of the scapula) to supply supraspinatus. A branch traverses the spinoglenoid notch to supply infraspinatus.
Nerve to Subclavius – The nerve to the Subclavius (or subclavian nerve) is a small filament, which arises from the point of junction of the fifth and sixth cervical nerves.
It descends to the subclavius muscle in front of the third part of the subclavian artery and the lower trunk of the plexus, and is usually connected by a filament with the phrenic nerve.
Long Thoracic Nerve – The long thoracic nerve supplies the Serratus Anterior muscle. This nerve arises by three roots from the fifth, sixth, and seventh cervical nerves (C5-C7) but the root from C7 may be absent. The roots from C5 and C6 pierce the Scalenus medius, while the C7 root passes in front of the muscle. The nerve descends behind the brachial plexus and the axillary vessels, resting on the outer surface of the Serratus anterior. It extends along the side of the thorax to the lower border of that muscle, supplying filaments to each of its digitations.
Thoracodorsal Nerve – The thoracodorsal nerve arises between the two subscapular nerves (upper & lower) off of the posterior cord, containing fibers from C6, C7, and C8 spinal segments. With the subscapular vessels it passes along the lateral border of subscapularis to supply latissimus dorsi.
Upper & Lower Subscapular Nerves – Upper and lower subscapular nerves arise on either side of the thoracodorsal nerve off of the posterior cord. The lower subscapular nerve is larger, passing downwards to supply subscapularis (C5,6) and teres major (C6,7).
Lateral Pectoral Nerve – Arises from the lateral cord, or from the anterior divisions of the upper and middle trunks just before these merge to form the lateral cord. It contains fibers from C5, C6 and C7 spinal segments. It pierces clavipectoral fascia to supply pectoralis major.
Medial Pectoral Nerve – Arises from the medial cord of the brachial plexus, containing fibers from C8 and T1 spinal segments. It passes between the axillary artery and vein to supply pectoralis minor and pectoralis major.
Medial Cutaneous Nerve of the Forearm – containing contribution from C8 & T1, it arises from the medial cord of the brachial plexus. In the middle of the arm it pierces deep fascia with the basilic vein, which it accompanies to the anterior surface of the elbow, dividing into anterior and posterior (ulnar) branches. The anterior branch supplies the medial part of the front of the forearm as far as the wrist. The posterior branch supplies the skin of the proximal three quarters of the posterior aspect of the forearm.
Medial Cutaneous Nerve of the Arm – arises from the medial cord of brachial plexus. It descends between axillary artery and vein before piercing the deep fascia to supply skin and fat on the medial side of the proximal half of the arm.