The brachial plexus: a map you memorise once

The brachial plexus is one of the most blindly memorised structures in anatomy, and one of the easiest to draw once you see it as layers. Five layers, centre to periphery:

Roots → trunks → divisions → cords → terminal branches

Roots

C5, C6, C7, C8 and T1, emerging between the anterior and middle scalene muscles.

Trunks

• Upper: C5 + C6
• Middle: C7 alone
• Lower: C8 + T1

Divisions

Each trunk splits into an anterior and a posterior division behind the clavicle. Nothing else happens here — except that every posterior division later collects into a single cord.

Cords

• Posterior cord: all three posterior divisions
• Lateral cord: anterior divisions of the upper and middle trunks
• Medial cord: anterior division of the lower trunk alone

The names describe position relative to the axillary artery, not to the body — a common slip.

Terminal branches

Branch	Cord
Musculocutaneous	Lateral
Median	Lateral + medial
Ulnar	Medial
Radial	Posterior
Axillary	Posterior

How I revise it

Blank paper, from memory, every three days for the first fortnight, then weekly. Drawing is harder than recognising, which is exactly why it sticks.