Schematic diagram of the brachial plexus. (By permission: Churchill Livingstone, Edinburgh, 1973, R. Warwick & P. Williams: Gray’s Anatomy 35th Edition © Longman Group UK Limited.)

The brachial plexus is a network of nerves, running from the spine, formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5–C8, T1). The brachial plexus passes through the cervico-axillary canal in the neck to reach the axilla (armpit region), and into the arm including the hand, innervating these regions.

Radial nerve (C5–8)

Radial nerve (and its branches) innervate the extensors of arm and forearm:

● ↯ triceps (all 3 heads)

● ↯ anconeus

● ↯ brachioradialis

● ↯ extensor carpi radialis longus & brevis (latter originates ≈ at terminal branch)

● ↯ supinator (originates near the terminal branch)

● ↳ continues into forearm as posterior interosseous nerve (C7, C8)

○ ↯ extensor carpi ulnaris

○ ↯ extensor digitorum

○ ↯ extensor digiti minimi

○ ↯ extensor pollicis brevis & longus

○ ↯ abductor pollicis longus

○ ↯ extensor indicis

see Brachial plexus injury