Which nerve innervates the triceps brachii?

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

Answer: (A)

The triceps brachii, a muscle in the posterior arm responsible for elbow extension, is innervated by the radial nerve. The radial nerve runs through the posterior arm and supplies the posterior compartment muscles, including all three heads of the triceps. Originating from the posterior cord of the brachial plexus (C5–T1), it travels in the area of the radial groove to reach the triceps and provide motor innervation for elbow extension.

The other nerves listed don’t supply the triceps: the musculocutaneous nerve innervates the anterior arm muscles (like biceps and brachialis), the median nerve mainly handles forearm flexors and some hand muscles, and the ulnar nerve mainly handles certain forearm flexors and intrinsic hand muscles. Thus, the radial nerve best fits as the nerve that innervates the triceps.