Brachial plexus

Roots

C5–T1 anterior rami (with variable C4 and T2 contributions).

Course

Roots unite into upper, middle and lower trunks between the scalene muscles; each trunk splits into anterior and posterior divisions behind the clavicle; divisions regroup as lateral, posterior and medial cords around the axillary artery; cords yield the five terminal branches in the axilla — musculocutaneous, axillary, radial, median and ulnar nerves.

Motor supply

Every muscle of the upper limb apart from the trapezius.

Sensory supply

The entire upper limb's cutaneous supply via its terminal branches.

Clinical relevance

Erb's palsy (C5–C6 traction — shoulder dystocia) hangs the arm in waiter's-tip position; Klumpke's palsy (C8–T1) claws the hand. Thoracic outlet syndrome and Pancoast tumours strike the lower trunk (C8–T1); the interscalene block targets its roots and trunks.

Related conditions

• Guillain–Barré syndrome