Complete Brachial Plexus Study Guide
A comprehensive guide to mastering the brachial plexus, from roots to terminal branches. This guide covers the anatomy, clinical correlations, and high-yield exam facts essential for medical students, physical therapists, and clinicians working with upper limb pathology.
Learning Objectives
- ✓Name and describe the organization of the brachial plexus from roots to branches
- ✓Identify the terminal branches and their muscle/sensory targets
- ✓Recognize clinical presentations of specific nerve injuries
- ✓Draw and label a complete brachial plexus diagram from memory
1. Overview and Organization
The brachial plexus is a network of nerves formed by the ventral rami of C5-T1 spinal nerves. It provides motor and sensory innervation to the upper limb. The plexus is organized into Roots, Trunks, Divisions, Cords, and Branches (remember: "Rugby Teams Drink Cold Beer" or "Robert Taylor Drinks Cold Beer").
Key Points
- •Roots: C5, C6, C7, C8, T1 (ventral rami)
- •Trunks: Superior (C5-6), Middle (C7), Inferior (C8-T1)
- •Divisions: Each trunk splits into anterior and posterior divisions
- •Cords: Lateral (anterior divisions of superior and middle trunks), Posterior (all three posterior divisions), Medial (anterior division of inferior trunk)
- •Cords are named by their relationship to the axillary artery
2. The Roots (C5-T1)
The roots emerge between the anterior and middle scalene muscles. Key branches arise directly from the roots before the plexus forms. These include nerves that innervate the "stabilizers" of the shoulder girdle.
Key Points
- •Dorsal scapular nerve (C5): Rhomboids, levator scapulae
- •Long thoracic nerve (C5-C7): Serratus anterior - injury causes winged scapula
- •Phrenic nerve contribution (C5): "C3, 4, 5 keeps the diaphragm alive"
- •Roots are between scalenes - vulnerable in thoracic outlet syndrome
3. The Trunks
The three trunks form in the posterior triangle of the neck. The suprascapular nerve is the only major branch from the trunks, arising from the superior trunk.
Key Points
- •Superior trunk (C5-6): Most commonly injured (Erb-Duchenne palsy)
- •Middle trunk (C7): No major branches from trunk itself
- •Inferior trunk (C8-T1): Less commonly injured alone
- •Suprascapular nerve (C5-6): Supraspinatus, infraspinatus - shoulder abduction and external rotation
4. The Divisions and Cords
Each trunk splits into anterior and posterior divisions behind the clavicle. These recombine to form three cords named by their position relative to the axillary artery. The lateral and medial cords supply flexors (anterior compartment); the posterior cord supplies extensors (posterior compartment).
Key Points
- •Lateral cord (C5-7): Anterior divisions of superior and middle trunks
- •Posterior cord (C5-T1): All three posterior divisions
- •Medial cord (C8-T1): Anterior division of inferior trunk only
- •Branches from cords include: lateral and medial pectoral nerves, thoracodorsal, subscapular nerves
5. Terminal Branches
The five terminal branches are the major nerves that supply the upper limb. Remember that the median nerve receives contributions from both lateral and medial cords, while the ulnar nerve is purely from the medial cord.
Key Points
- •Musculocutaneous nerve (C5-7, lateral cord): Biceps, brachialis, coracobrachialis; sensory to lateral forearm
- •Median nerve (C5-T1, lateral + medial cords): Forearm flexors (except FCU and medial FDP), thenar muscles (LOAF)
- •Ulnar nerve (C8-T1, medial cord): FCU, medial FDP, hypothenar muscles, interossei
- •Radial nerve (C5-T1, posterior cord): All extensors of arm and forearm
- •Axillary nerve (C5-6, posterior cord): Deltoid, teres minor; sensory to "regimental badge" area
6. Clinical Correlations
Brachial plexus injuries are classified by level (roots, trunks, cords, branches) and mechanism. Understanding the clinical presentation helps localize the lesion and predict prognosis.
Key Points
- •Erb-Duchenne palsy (C5-6, upper trunk): "Waiter's tip" - arm adducted, internally rotated, forearm pronated
- •Klumpke palsy (C8-T1, lower trunk): Claw hand - intrinsic muscle weakness, sensory loss in medial arm
- •Posterior cord injury: Wrist drop (radial), weak shoulder abduction (axillary)
- •Long thoracic nerve injury: Winged scapula - serratus anterior paralysis
High-Yield Facts
- ★Lateral cord = C5-7, gives off musculocutaneous and lateral contribution to median
- ★Medial cord = C8-T1, gives off ulnar and medial contribution to median
- ★Posterior cord = "STAR" - Subscapular (upper and lower), Thoracodorsal, Axillary, Radial
- ★Long thoracic nerve: "wings" the scapula, runs on serratus anterior
- ★Erb's point is where C5-6 join to form the superior trunk
- ★Axillary nerve wraps around surgical neck of humerus - vulnerable to fracture/dislocation
Practice Questions
1. A patient presents with inability to flex the elbow and absent biceps reflex. Sensory loss is present over the lateral forearm. Which nerve is affected?
2. A newborn following a difficult delivery presents with the arm adducted, internally rotated, and the forearm pronated. Which roots are most likely affected?
3. Which nerve is at risk during surgical dissection of the axillary lymph nodes, and what would its injury cause?
FAQs
Common questions about this topic
Draw it repeatedly until you can reproduce it from memory. Use the mnemonic "Rugby Teams Drink Cold Beer" (Roots, Trunks, Divisions, Cords, Branches). Associate each terminal nerve with a specific movement and test yourself clinically on study partners.
Nerves that supply proximal structures (like scapular stabilizers) branch off early at the root or trunk level. Terminal nerves that travel to the arm and hand branch from the cords, which have reorganized the fibers appropriately for anterior (flexor) and posterior (extensor) compartments.