Brachial Plexus Explained: Formation, Branches, Diagram & Clinical Cases (Erb’s vs Klumpke’s)

The brachial plexus is a nerve network from C5–T1 supplying motor and sensory functions to the upper limb. It follows a structured pathway, roots, trunks, divisions, cords, and branches, ensuring efficient nerve distribution and minimizing total limb paralysis risk.

Its key terminal branches (MARMU) control major arm and hand functions. Clinically, injuries cause conditions like Erb’s palsy (upper trunk, “waiter’s tip”) and Klumpke’s palsy (lower trunk, “claw hand”), making it a high-yield topic for medical exams.

Brachial Plexus 

The brachial plexus is a critical nerve network formed by spinal nerves C5 to T1. It supplies motor and sensory functions to the entire upper limb. 

In simple terms, the brachial plexus is the nerve junction box for your arm and hand. Originating from spinal nerves C5-T1, it enables all upper limb movements. These nerves weave through the neck and armpit, forming an intricate system. 

This design ensures widespread nerve supply, protecting against total limb paralysis from single nerve damage. Its complex structure is vital for understanding neurology and common nerve injuries, making it a frequent topic in medical exams.

Brachial Plexus Formation

The brachial plexus forms in a specific five-stage sequence:

• Roots: These are the anterior rami of spinal nerves C5, C6, C7, C8, and T1.

• Trunks: Roots combine to form three trunks: Superior (C5+C6), Middle (C7), and Inferior (C8+T1).

• Divisions: Each trunk splits into an anterior and a posterior division. Anterior divisions serve flexor muscles; posterior divisions serve extensors.

• Cords: Divisions rejoin around the axillary artery to form three cords: Lateral, Posterior, and Medial.

• Terminal Branches: The cords give rise to five main nerves for the upper limb.

The Brachial Plexus's Branches

Branches arise from roots, trunks (supraclavicular), and cords (infraclavicular).

Supraclavicular Branches

• From Roots: Dorsal Scapular Nerve (C5), Long Thoracic Nerve (C5, C6, C7).

• From Superior Trunk: Suprascapular Nerve (C5, C6).

Infraclavicular Branches (Terminal Branches)

These are key: Musculocutaneous, Axillary, Radial, Median, and Ulnar nerves (MARMU).

• Musculocutaneous Nerve (C5, C6, C7): Supplies anterior arm muscles.

• Axillary Nerve (C5, C6): Supplies deltoid and teres minor.

• Radial Nerve (C5-T1): Supplies posterior arm and forearm muscles.

• Median Nerve (C5-T1): Supplies most forearm flexors and some hand muscles.

• Ulnar Nerve (C7, C8, T1): Supplies specific forearm flexors and most intrinsic hand muscles.

Brachial Plexus Relations

The plexus has key anatomical relationships. It lies between the scalene muscles in the neck. Trunks are in the posterior triangle, with the inferior trunk near the subclavian artery. In the axilla, cords surround the second part of the axillary artery, enclosed by the axillary sheath, behind the pectoralis minor.

Erb's Palsy and Klumpke's Palsy Comparison 

Brachial plexus injuries cause distinct clinical presentations. Erb-Duchenne Palsy impacts the upper plexus, causing a "waiter's tip" posture. Klumpke's Palsy affects the lower plexus, leading to a "claw hand." Winging of the scapula results from long thoracic nerve damage.