Which nerve supplies the majority of extensor muscles in the forearm?

• A. Median
• B. Ulnar
• C. Radial
• D. Musculocutaneous

Answer: (C)

Forearm extensors belong to the posterior compartment and are mainly innervated by the radial nerve. After the radial nerve passes the elbow, its deep branch becomes the posterior interosseous nerve, which supplies most of the extensor muscles such as those that extend the fingers and thumb (including extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus and brevis, and abductor pollicis longus) along with the supinator. The radial nerve also gives innervation to the brachioradialis and the extensor carpi radialis longus before it divides, but the vast majority of forearm extensors receive their motor input from this radial lineage. In contrast, the median nerve mainly controls forearm flexors, the ulnar nerve supplies some wrist/finger flexors and intrinsic hand muscles, and the musculocutaneous nerve innervates the anterior arm flexors. Therefore, the nerve that supplies the majority of forearm extensor muscles is the radial nerve.