The radial nerve is the nerve of the posterior arm and forearm and arises from the posterior cord of the brachial plexus. It supplies the muscles of the posterior arm and forearm, as well as sensation to the skin overlying this region. At the hand it supplies sensation to the dorsal three and a half fingers excluding the nailbeds, via its superficial branch.

The radial nerve (C5-T1) is a branch of the posterior cord of the brachial plexus. It runs behind the third part of the brachial artery then passes through the triangular space. This space is bordered by the lateral head of the triceps laterally, the long head medially, and the teres major muscle superiorly. It supplies the posterior compartment of the arm i.e. triceps brachii, although the long head has been shown to be supplied by the axillary nerve. The posterior and inferior lateral cutaneous nerves of the arm, and the posterior cutaneous nerve of the forearm originate in the arm.

 

The nerve then continues in the spiral groove of the humerus, and descends to eventually pierce the lateral intermuscular septum to emerge at the elbow anterior to the lateral epicondyle. It runs between the brachialis and brachioradialis muscles (it supplies brachioradialis, a flexor of the elbow and supinator of the forearm that separates the flexor and extensor compartment of the forearm). It then enters the supinator muscle. Here it divides into the posterior interosseus nerve and the superficial branch of the radial nerve. The posterior interosseus branch descends along the interosseus membrane, anterior to the extensor pollicis longus muscle, and supplies the posterior compartment of the forearm (anconeus, extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, abductor pollicis longus, extensor carpi ulnaris, extensor carpi radialis longus and brevis). The nerve will finish at the dorsal surface of the hand. The superficial branch is also given off within the supinator, and it runs distally to the hand to supply sensation to the radial 3 and a half fingers (excluding the nail-beds, which are supplied by the median nerve). 

Developmental precursor- Alar and basal plate of C5-T1 spinal nerves

Origin- C5-T1

Branches- Posterior interosseus nerve, posterior cutaneous nerve of the arm, posterior cutaneous nerve of the forearm, superficial branch

Muscles supplied- Lateral and medial head of triceps, extensor compartment of the forearm (and brachioradialis)

Dermatome- Entire posterior surface of the arm and forearm, and the radial 3 and half fingers (excluding nail-beds) on the dorsal aspect of the hand. 

 Recall the radial nerve arises from the posterior cord of the brachial plexus, it runs around the back of the humerus in the spiral groove, and supplies the muscle of the posterior compartment of the arm and forearm.

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