Which nerve innervates the biceps brachii?

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

Answer: (B)

Understanding which nerve supplies the biceps brachii connects the muscle’s function with its nerve supply. The biceps brachii is in the anterior (flexor) compartment of the arm and mainly controls elbow flexion and forearm supination. Its motor innervation comes from the musculocutaneous nerve, which arises from the lateral cord of the brachial plexus (carrying fibers from C5–C7) and travels through the arm to innervate the elbow flexors: biceps brachii, brachialis, and coracobrachialis. The radial nerve supplies the posterior compartment (like the triceps) and some forearm extensors, but not the biceps. The median and ulnar nerves primarily innervate most forearm flexors and hand muscles, not the primary motor supply to the biceps. Therefore, the musculocutaneous nerve is the correct innervation for the biceps brachii.