Anatomy I · Topic 2 of 4
Brachial plexus
30 min read
The brachial plexus is formed by the anterior rami of C5–T1 and supplies the entire upper limb. It is organised as roots, trunks, divisions, cords and terminal branches — “Real Texans Drink Cold Beer”.
Structure
Roots C5–T1 lie between the anterior and middle scalenes. They form the upper (C5–6), middle (C7) and lower (C8–T1) trunks above the clavicle. Each trunk splits into anterior and posterior divisions behind the clavicle.
The cords — lateral, posterior and medial — are named by their relationship to the axillary artery.
Five terminal branches
Each terminal branch has a characteristic motor territory and injury pattern.
- Musculocutaneous (C5–7) — elbow flexors; loss weakens flexion and supination
- Axillary (C5–6) — deltoid and teres minor; injured in surgical neck fractures
- Radial (C5–T1) — extensors; mid-shaft humerus fracture causes wrist drop
- Median (C5–T1) — forearm flexors, thenar muscles; carpal tunnel syndrome
- Ulnar (C8–T1) — intrinsic hand muscles; medial epicondyle injury causes claw hand
Plexus injuries
Erb palsy (C5–6, upper trunk) produces the “waiter’s tip” posture: arm adducted, medially rotated and the forearm pronated. Klumpke palsy (C8–T1, lower trunk) produces a claw hand and may be accompanied by Horner syndrome.
High-yield points
- Erb palsy = upper trunk = waiter’s tip.
- Klumpke palsy = lower trunk = claw hand ± Horner syndrome.
- Long thoracic nerve (C5–7) injury causes a winged scapula.