Brachial Plexus: Anatomy, Branches, and Clinical Significance
Hacı Mert Gökhan
@hacimertgokhan
Overview
The brachial plexus is a network of nerves that supplies the entire upper limb. It is formed by the anterior rami of spinal nerves C5 to T1 and carries both motor and sensory fibers to the shoulder, arm, forearm, and hand.
The Five Stages
A reliable way to remember its structure is the sequence Roots → Trunks → Divisions → Cords → Branches:
- Roots (C5–T1): Five anterior rami emerge between the scalene muscles of the neck.
- Trunks: The roots combine into the superior (C5–C6), middle (C7), and inferior (C8–T1) trunks.
- Divisions: Each trunk splits into an anterior and a posterior division behind the clavicle.
- Cords: The divisions regroup around the axillary artery into the lateral, posterior, and medial cords.
- Branches: The cords give rise to the five major terminal nerves.
The Five Terminal Branches
- Musculocutaneous nerve – flexor muscles of the arm.
- Axillary nerve – deltoid and teres minor.
- Radial nerve – extensors of the arm and forearm.
- Median nerve – most forearm flexors and thenar muscles.
- Ulnar nerve – most intrinsic muscles of the hand.
Clinical Significance
Injury patterns map predictably onto this anatomy. Erb's palsy results from damage to the upper trunk (C5–C6), producing the classic "waiter's tip" posture. Klumpke's palsy affects the lower trunk (C8–T1) and impairs the small muscles of the hand. Knowing where a lesion sits along the plexus allows precise localization of weakness and sensory loss.
Summary
The brachial plexus translates five spinal roots into five terminal nerves through an orderly five-step reorganization. Mastering this map is the key to understanding upper-limb innervation and diagnosing nerve injuries.
For educational purposes only; not a substitute for medical advice.