Breast · Interactive 3D

Brachial plexus

The brachial plexus from roots to terminal branches: C5–T1 roots, the upper, middle and lower trunks, anterior and posterior divisions, the lateral, posterior and medial cords, and the nerves each gives off.

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Anatomy after Radiopaedia (brachial plexus).

What to look at

1Read it right to left: the five roots emerge between scalenus anterior and medius, form three trunks, split into anterior and posterior divisions behind the clavicle, and regroup as three cords named for their position around the axillary artery.
2Anterior divisions supply the flexor compartments; posterior divisions supply the extensors — so the posterior cord carries the axillary and radial nerves.
3Branches from the roots (dorsal scapular C5, long thoracic C5–7) and the upper trunk (suprascapular, nerve to subclavius) are the clues that place a lesion at root or trunk level — a favourite Part A discriminator.
4About half of people vary: a prefixed plexus starts at C4, a postfixed one reaches T2.

Hotspots

1C5 root — Upper root; with C6 forms the upper trunk. Gives the dorsal scapular nerve and contributes to the phrenic and long thoracic nerves.
2C6 root — Joins C5 to form the upper trunk; contributes to the long thoracic nerve and the nerve to subclavius.
3C7 root — Continues alone as the middle trunk; last contribution to the long thoracic nerve.
4C8 root — With T1 forms the lower trunk — the roots most often avulsed in a traction injury with the arm abducted.
5T1 root — Lower root; a lesion here gives intrinsic hand weakness and, if the sympathetic rami are involved, Horner’s syndrome.
6Dorsal scapular nerve (C5) — From the posterior aspect of the C5 root to the rhomboids — a root-level branch, so rhomboid function helps localise the injury.
7Long thoracic nerve (C5–7) — From the posterior aspects of C5, C6 and C7, descending on serratus anterior; winged scapula when injured.
8Upper trunk (C5, C6) — Gives the suprascapular nerve and the nerve to subclavius before dividing; Erb’s point lesions injure it.
9Middle trunk (C7) — The continuation of C7; divides into anterior and posterior divisions behind the clavicle.
10Lower trunk (C8, T1) — Its anterior division continues as the medial cord; Klumpke’s palsy follows a lower trunk injury.
11Suprascapular nerve — From the upper trunk to supraspinatus and infraspinatus — shoulder abduction initiation and external rotation.
12Lateral cord — Anterior divisions of the upper and middle trunks. Branches: lateral pectoral nerve, musculocutaneous nerve and the lateral root of the median nerve.
13Posterior cord — All three posterior divisions. Branches: upper subscapular, thoracodorsal and lower subscapular nerves, then the axillary and radial nerves.
14Medial cord — Anterior division of the lower trunk. Branches: medial pectoral, medial cutaneous nerves of arm and forearm, ulnar nerve and the medial root of the median nerve.
15Lateral pectoral nerve — From the lateral cord (C5–7) to pectoralis major; loops with the medial pectoral nerve as the ansa pectoralis.
16Musculocutaneous nerve (C5–7) — Terminal branch of the lateral cord: coracobrachialis, biceps and brachialis, then the lateral cutaneous nerve of the forearm.
17Median nerve — Formed by a lateral root (lateral cord, C5–7) and a medial root (medial cord, C8–T1) in front of the axillary artery.
18Ulnar nerve (C8, T1 ± C7) — Continuation of the medial cord down the medial arm to the cubital tunnel.
19Radial nerve (C5–T1) — Continuation of the posterior cord — the largest branch of the plexus, into the spiral groove.
20Axillary nerve (C5, C6) — From the posterior cord through the quadrangular space to deltoid and teres minor.
21Thoracodorsal nerve (C6–8) — From the posterior cord to latissimus dorsi, between the upper and lower subscapular nerves.
22Medial cutaneous nerve of the forearm — From the medial cord (C8, T1) — sensation over the medial forearm; spared in a pure ulnar nerve lesion at the elbow, lost in a lower trunk or medial cord lesion.

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