Overview
This lecture covers the anatomy and clinical importance of the brachial plexus and its five terminal branches, detailing their origin, course, supply, injury patterns, and relevant clinical features.
Structure of the Brachial Plexus
- The brachial plexus is formed by spinal nerve roots C5-T1 in the neck.
- It organizes into three cords: lateral, posterior, and medial.
- Five terminal branches arise: musculocutaneous, axillary, radial, median, and ulnar nerves.
- The cords and nerves surround the third part of the axillary artery, with an "M-shaped" nerve pattern anteriorly.
Musculocutaneous Nerve (C5-C7)
- Origin: lateral cord.
- Course: Pierces coracobrachialis, runs beneath biceps, ends as lateral cutaneous nerve of forearm.
- Supplies anterior arm muscles (biceps, brachialis, coracobrachialis) and lateral forearm skin.
- Injury: Rare; causes weak elbow flexion/supination, numbness lateral forearm, arm muscle wasting.
Axillary Nerve (C5-C6)
- Origin: posterior cord.
- Course: Passes through quadrangular space, around surgical neck of humerus.
- Supplies deltoid/teres minor muscles and sergeant's patch skin.
- Injury: From humerus fracture/dislocation/crutch use; causes weak abduction, deltoid wasting, numbness over deltoid.
Radial Nerve (C5-T1)
- Origin: posterior cord.
- Course: Travels in spiral groove of humerus, divides in forearm into superficial (sensory) and deep (motor) branches.
- Supplies posterior arm/forearm muscles and dorsum of hand/lateral 3 fingers.
- Injury: From fractures, compression, or trauma; leads to wrist drop and sensory loss in radial distribution.
Median Nerve (C5-T1)
- Origin: lateral and medial cords.
- Course: Runs with brachial artery, enters forearm, passes through carpal tunnel.
- Supplies most anterior forearm muscles and thenar/LOAF hand muscles; sensory to lateral palm, fingers.
- Injury: Supracondylar fractures, carpal tunnel, or trauma; causes weak pronation, thenar wasting, hand of benediction.
Ulnar Nerve (C8-T1)
- Origin: medial cord.
- Course: Medial to brachial artery, passes behind medial epicondyle, enters hand via Guyon's canal.
- Supplies medial forearm muscles and most intrinsic hand muscles; sensory to medial hand/little finger.
- Injury: From medial epicondyle trauma or compression; causes claw hand and hypothenar wasting.
Clinical Anatomy and Nerve Injuries
- Sensory distribution divided into dermatomes (spinal roots) and peripheral nerve zones.
- Types of nerve injuries: neurapraxia (stretch), axonotmesis (partial sever), neurotmesis (complete sever), avulsion, neuroma.
- Motor testing by myotomes (movement testing individual nerve roots).
Key Terms & Definitions
- Brachial plexus — nerve network supplying the upper limb, formed by C5-T1 roots.
- Dermatome — skin area supplied by a single spinal nerve root.
- Myotome — group of muscles controlled by a single spinal nerve.
- Neurapraxia — temporary nerve conduction block (no tear).
- Axonotmesis/Neurotmesis — partial/complete nerve fiber disruption.
Action Items / Next Steps
- Review diagrams of the brachial plexus and nerve injury patterns.
- Practice identifying nerve injury presentations and related clinical signs.
- Study upper limb dermatomes and myotomes for practical exams.