Which nerve innervates the triceps brachii?

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

Answer: (C)

The triceps brachii is a major elbow extensor located in the posterior arm, and it gets its nerve supply from the radial nerve. The radial nerve arises from the posterior cord of the brachial plexus (primarily C6–C8) and innervates the muscles that extend the elbow in the arm and forearm, including all three heads of the triceps. It travels in the radial groove with the profunda brachii artery, reinforcing its role as the key motor nerve for posterior-arm and forearm extensors. In contrast, the ulnar nerve mostly serves intrinsic hand muscles and some forearm flexors, the median nerve largely innervates the anterior forearm muscles and some hand muscles, and the musculocutaneous nerve innervates the anterior arm flexors. Therefore, the radial nerve is the correct innervation for the triceps.