Brachial Plexus
The brachial plexus (C5–T1) is the neural network supplying the entire upper limb. Its five-level organisation — roots, trunks, divisions, cords, branches — is a framework that maps every nerve injury to its anatomical level and predicts the resulting deficit.
✦ The Mnemonic
"Reading Textbooks Develops Clinical Brilliance"
The five levels of the brachial plexus — proximal to distal
Clinical Breakdown
The terminal branches can be remembered as "My Aunt Really Misses Understanding" — Musculocutaneous (lateral cord), Axillary (posterior cord), Radial (posterior cord), Median (medial and lateral cords), Ulnar (medial cord). Note the median nerve has a dual-cord origin, giving it a characteristic V-shaped formation around the axillary artery on cross-section.
Erb's palsy (C5–C6) — upper trunk injury, typically from traction during delivery or a fall. The arm hangs in the 'waiter's tip' posture: adducted, internally rotated, elbow extended, forearm pronated. The deltoid, biceps, and supinator are primarily affected.
Klumpke's palsy (C8–T1) — lower trunk injury from hyperabduction of the arm. Intrinsic hand muscle paralysis produces a claw hand. When the T1 ramus is also injured, loss of sympathetic fibres causes a Horner's syndrome on the same side (ptosis, miosis, anhidrosis).
⭐ Clinical Pearl
Long thoracic nerve (C5–7) arises directly from the roots and is not part of the trunks/cords sequence. It supplies serratus anterior. Injury produces winging of the scapula (medial border prominent at rest, worsens with forward flexion). It is vulnerable in radical mastectomy and axillary lymph node dissection.
⚠ Exam Trap
Pre-ganglionic vs post-ganglionic root avulsion: pre-ganglionic injuries (root torn from cord) cannot regenerate and have no Tinel's sign; sensory nerve action potentials are PRESERVED on nerve conduction studies (because the dorsal root ganglion is intact). This is a key distinction in planning brachial plexus surgery.