Nerve	Anatomy	Function		Risk factors for injury
Axillary	From brachial plexus, around humeral head, through the quadrilateral space to deltoid/teres minor Quadrilateral space boundaries: humeral neck, teres major and minor, long head of triceps	Motor: deltoid, teres minor Sensory: skin over lower half of the deltoid		Humeral head compresses nerve during extreme abduction Upward pressure through the axilla Shoulder dislocation Compression in quadrilateral space
Long thoracic	C5 to C7 merge, travel between clavicle and first rib through axilla to serratus anterior muscle Long nerve: 20 to 22 cm	Motor: serratus anterior Sensory: none		Sudden upper extremity traction Shoulder depression with contralateral neck flexion Prolonged compression (backpacker's palsy)
Median	Brachial plexus down anterior arm, at antecubital fossa passes through radial tunnel, dives between two heads of pronator muscle, under flexor digitorum superficialis, through carpal tunnel	Motor: Injury at elbow or forearm: Weak wrist flexion, no interphalangeal flexion of thumb, index, and long digit Injury at wrist: none or weak thumb abduction Sensory: Injury at elbow: proximal forearm pain Injury at wrist: sensory loss in the thumb, radial 2.5 digits, and thenar eminence		Injury at elbow or forearm: radial tunnel, within pronator teres muscle, under flexor digitorum superficialis Injury at wrist: carpal tunnel syndrome
Musculocutaneous	C5 to C7 merge into lateral cord brachial plexus, goes through axilla, under coracobrachialis, through biceps and under deep fascia at the elbow	Motor: Injury at shoulder: loss in biceps, coracobrachialis, and brachialis Injury at elbow: none Sensory: radial side of forearm (dorsal and volar), but not hand		Shoulder dislocation Hypertrophy of the coracobrachialis Deep brachial fascia of elbow as nerve exits biceps (sensory symptoms only)
Radial	From brachial plexus, through axilla, down posterior arm until it circles toward anterior arm at spiral groove of the humerus; down anterior arm and enters radial tunnel just above the lateral epicondyle Divides into superficial and deep (posterior interosseus nerve) branches	Motor: Injury in axilla: loss of elbow flexion; weak wrist and digit extension; weak forearm supination Injury at elbow: superficial branch (radial tunnel): forearm pain, normal motor; posterior interosseus nerve: weak or no wrist extension Injury at wrist: no motor loss Sensory: variable sensory loss in distal forearm or hand Injury at elbow: no sensory loss; possible pain with repetitive forearm supination		Injury in axilla or proximal humerus (fracture) Injury at elbow: radial tunnel or area of proximal radius (fracture or dislocation); two nerve branches from elbow have injury potential, posterior interosseus nerve has mostly motor loss and the superficial branch has only sensory change (pain)
Spinal accessory	Emerges through sternocleidomastoid muscle, across posterior neck, dives under trapezius	Motor: trapezius Sensory: none		Very superficial course in posterior neck and directly under the trapezius muscle
Suprascapular	From upper trunk brachial plexus, through posterior triangle, across top of scapula and through scapular notch, down posterior aspect scapula and across scapular spine to supraspinatus, infraspinatus	Motor: supraspinatus, infraspinatus Sensory: acromioclavicular and glenohumeral joints		Entrapment under transverse scapular ligament that covers the suprascapular notch Injury as it crosses scapular spine or under spinoglenoid ligament
Ulnar	From brachial plexus down anterior arm; just above medial epicondyle it passes to the posterior compartment and into the cubital tunnel; down ulnar side of forearm into Guyon canal (boundaries are hamate and pisiform bones); splits into deep (motor) and superficial (sensory) branches in canal	Motor: no loss or weak thumb adduction, weak digit abduction, and adduction toward center of long digit Sensory: Injury at elbow: pain ulnar side of forearm with or without paresthesias in ulnar digits Injury at wrist: paresthesias in ulnar digits		Injury at elbow or forearm: cubital tunnel, ulnar nerve irritation with medial collateral ligament deficiency Injury at wrist: Guyon canal
Upper trunk cervical plexus	Nerve roots C5 and C6 as they exit vertebral foramina and form upper trunk brachial plexus	Motor: infraspinatus, supraspinatus, biceps, and deltoid Sensory: C5 and C6 dermatomes		No protective coverings (epineurium and perineurium) on the nerves after they exit the foramina Increased risk of stretch injury at neck and shoulder regions Contusion or compression of upper trunk at Erb point