The Brachial Plexus: Roots to Branches

1. Introduction

The brachial plexus is a network of nerves formed by the anterior rami of cervical nerves C5-C8 and thoracic nerve T1. It provides sensory and motor innervation to the upper extremity.

2. Structure (mnemonic: Robert Taylor Drinks Cold Beer)

• Roots: C5, C6, C7, C8, T1.
• Trunks: Superior (C5-C6), Middle (C7), Inferior (C8-T1).
• Divisions: Each trunk divides into anterior (flexor) and posterior (extensor) divisions.
• Cords: Lateral, Medial, and Posterior (named relative to the axillary artery).
• Terminal Branches: Musculocutaneous, Axillary, Radial, Median, and Ulnar nerves.

3. Major Nerves

• Radial Nerve: Supplies the triceps and wrist extensors. Injury leads to "wrist drop."
• Median Nerve: Supplies most forearm flexors and the thenar eminence. Associated with Carpal Tunnel Syndrome.
• Ulnar Nerve: Supplies intrinsic hand muscles. Injury leads to "claw hand."

4. Clinical Cases

• Erb's Palsy: Injury to upper trunks (C5-C6), resulting in "waiter's tip" position.
• Klumpke's Palsy: Injury to lower trunks (C8-T1), affecting hand intrinsics.

5. Questions

1. Which nerve is formed by the medial and lateral cords?
2. Loss of sensation in the axillary region suggests damage to which nerve?
3. Which cord gives rise to the radial nerve?