RootsThe five anterior rami that form the plexus. They belong to spinal nerves C5, C6, C7, C8 and T1.
Upper trunkFormed by roots C5 and C6. Also called the superior trunk.
DivisionsEach trunk splits into an anterior and a posterior division. There are six in all. They regroup to form the cords.
Lateral cordFormed by the upper and middle trunks' anterior divisions (C5 to C7).
Posterior cordFormed by all three posterior divisions (C5 to T1).
Medial cordThe continuation of the anterior division of the lower trunk (C8, T1).
Median nerveA terminal branch formed from both the lateral and medial cords. Its two roots make the middle of the M shape.
Radial nerveA large terminal branch of the posterior cord. It runs down the arm, carrying both skin sensation and motor fibers.
Ulnar nerveA terminal branch of the medial cord. It runs down the arm beside the median nerve.
Roots, trunks, divisions: 5 2
Middle trunkThe continuation of root C7 alone.
Lower trunkFormed by roots C8 and T1. Also called the inferior trunk.
The five nerves: 5 2
Musculocutaneous nerveA terminal branch of the lateral cord.
Axillary nerveA terminal branch of the posterior cord, going to the armpit region.
How this list was compiled: Read 2026-09-26. Wikipedia, Brachial plexus, https://en.wikipedia.org/wiki/Brachial_plexus : formed by the anterior rami of C5 to T1; five roots, three trunks, six divisions, three cords and five terminal branches; C5 and C6 forming the upper (superior) trunk, C7 the middle trunk, C8 and T1 the lower (inferior) trunk; each trunk splitting into anterior and posterior divisions; the posterior cord from the three posterior divisions, the lateral cord from the anterior divisions of the upper and middle trunks, the medial cord continuing the anterior division of the lower trunk; the terminal branches musculocutaneous, axillary, radial, median and ulnar; the M shape of musculocutaneous nerve, lateral cord, median nerve, medial cord and ulnar nerve; the mnemonic roots, trunks, divisions, cords, branches. OpenStax Anatomy and Physiology 2e 13.4, https://openstax.org/books/anatomy-and-physiology-2e/pages/13-4-the-peripheral-nervous-system : the radial nerve with the axillary nerve going to the armpit, paralleled by the ulnar and median nerves; the radial nerve carrying both cutaneous sensation and motor fibers. Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
A brachial plexus diagram labeled as the usual flat schematic: five roots from C5 to T1 on the left, merging and regrouping through trunks, divisions and cords into the five nerves of the arm. It covers the homework: label the nerves of the brachial plexus.
Read the full guide
Left to right
The five roots (C5 to T1) join into three trunks: upper, middle and lower. Each trunk splits into an anterior and a posterior division. The divisions regroup into three cords: lateral, posterior and medial.
The five nerves
The lateral cord gives the musculocutaneous nerve, the posterior cord the axillary and radial nerves, and the medial cord the ulnar nerve. The median nerve takes a root from both the lateral and medial cords, making the M shape.
What are the five terminal nerves of the brachial plexus?
The musculocutaneous, axillary, radial, median and ulnar nerves. The lateral cord gives the musculocutaneous, the posterior cord the axillary and radial, the medial cord the ulnar, and the median comes from both the lateral and medial cords.
Which roots form the brachial plexus?
The anterior rami of spinal nerves C5, C6, C7, C8 and T1. In some people C4 or T2 also contribute.
How are the cords named?
By their position around the axillary artery: lateral, posterior and medial. The posterior cord takes all three posterior divisions.