The brachial plexus is formed by the anterior (ventral) rami of spinal nerves C5 to T1 and supplies the upper limb. These roots carry both motor and sensory fibers.
The roots join to form three trunks:
The trunks cross the floor of the posterior triangle of the neck and emerge between the anterior and middle scalene muscles.
Each trunk divides into an anterior division and a posterior division, which then reorganize into cords:
The cords are formed as follows:
The cords are named for their relationship to the axillary artery. They pass over the first rib near the apex of the lung and continue under the clavicle, posterior to the subclavian artery.
| Branch | Origin | Distribution |
|---|---|---|
| Median Nerve | C6-T1, from medial and lateral cords | Motor to forearm flexors and thenar muscles including pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, lateral 2 lumbricals, opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis. Sensory innervation to lateral 3.5 digits on the palmar surface and also including fingertips on the dorsal side of the thumb, index finger, middle finger and lateral half of ring finger. Its branch, the anterior interosseous nerve, supplies flexor pollicis longus, pronator quadratus, and the lateral half of flexor digitorum profundus. |
| Ulnar Nerve | C8-T1, medial cord only | Forearm muscles: medial half of the flexor digitorum profundus, flexor carpi ulnaris. Superficial branch supplies palmaris brevis and sensory to medial 1.5 fingers on palmar and dorsal surfaces including the fingertips. Deep branch supplies hypothenar muscles (abductor digiti minimi, flexor and opponens digiti minimi); adductor pollicis; deep head of the flexor pollicis brevis; 3rd and 4th lumbricals; and all palmar and dorsal interossei muscles. |
| Musculocutaneous Nerve | C5-7, lateral cord only | Motor to biceps brachii, coracobrachialis, brachialis; continues as the lateral antebrachial cutaneous nerve to supply the skin of the lateral upper forearm. |
| Radial Nerve | C5-T1; posterior cord only | All extensor muscles of the arm and forearm. Above the elbow it supplies the triceps, anconeus, brachioradialis, and extensor carpi radialis longus. Sensory innervation to parts of posterior arm and forearm. At the elbow it divides into superficial and deep branches: superficial supplies the dorsal aspect of lateral 3.5 fingers (including continuous dorsal hand) and also a small area on the palmar aspect of the base of the thumb; deep supplies supinator and extensor carpi radialis brevis. As the posterior interosseous nerve, it supplies the extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis. |
| Axillary Nerve | C5,6; posterior cord only | Motor to deltoid and teres minor muscles. Sensory supply to shoulder joint and skin over the lateral and posterior part of the deltoid muscle. |
| Dorsal Scapular Nerve | Direct branch from C5 root | Motor to rhomboids major and minor and levator scapulae. |
| Long Thoracic Nerve | Direct branch from roots C5,6 and 7 | Serratus anterior |
| Suprascapular Nerve | Branch from upper trunk, C5,6 | Supraspinatus and infraspinatus muscles, sensory to shoulder joint |
| Lateral Pectoral Nerve | Branch from lateral cord, C5,6 and 7 | Pectoralis major muscle |
| Medial Pectoral Nerve | Branch from the medial cord, C8, T1 | Pectoralis minor muscle and major |
| Medial Brachial Cutaneous Nerve | Branch from the medial cord, C8, T1 | Sensory to lower, medial arm |
| Medial Antebrachial Cutaneous Nerve | Branch from the medial cord, C8, T1 | Sensory to medial forearm |
| Nerve to Subclavius | Branch from the upper trunk, C5,6 | Subclavius muscle |
| Phrenic Nerve | Direct from C3,4 and 5 roots (connected to both cervical and brachial plexuses) | Supplies the diaphragm and mediastinal pleura and pericardium |
| Upper Subscapular Nerve | Branch from posterior cord, C5,6 | Subscapularis muscle |
| Lower Subscapular Nerve | Branch from posterior cord, C5,6 | Subscapularis and Teres major muscles |
| Middle Subscapular or Thoracodorsal Nerve | Branch from posterior cord, C6,7,8 | Latissimus dorsi |
This results from damage to the superior trunk (C5 and C6) of the brachial plexus. Common causes include birth injury (when the head and shoulder are forcibly separated), disc herniation, and traffic accidents.
Nerves commonly affected include the axillary, suprascapular, and musculocutaneous nerves.
A classic finding is the waiter’s tip deformity, in which the arm is adducted and medially rotated at the shoulder. There may also be sensory loss in the musculocutaneous distribution over the lateral forearm.
This results from damage to the inferior trunk (C8 and T1) of the brachial plexus. Causes include birth injury and traction injuries in which the upper limb is forcefully abducted above the head (for example, grabbing an object while falling). It can also occur with thoracic outlet syndrome.
It presents with ulnar nerve palsy, weakness of the intrinsic muscles of the hand, and loss of sensation on the medial forearm and medial 1.5 digits. An ulnar claw hand may be seen, affecting the medial 1.5 digits.
Ape hand deformity is also described. Ape hand is an inability to abduct the thumb. It is seen in median nerve lesions with paralysis of the opponens pollicis muscle.
Patients may have Horner’s Syndrome.
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