Which muscle group acts as the prime mover for elbow flexion, and what is its nerve supply?

• A. Triceps brachii; radial nerve.
• B. Brachialis; radial nerve.
• C. Biceps brachii; musculocutaneous nerve (C5-C7).
• D. Biceps brachii; axillary nerve.

Answer: (C)

Elbow flexion is produced by muscles that cross the elbow on the anterior aspect of the arm. The biceps brachii is the strongest elbow flexor when the forearm is supinated, because its tendon crosses the radius and its line of pull creates a powerful flexion moment at the elbow while also aiding supination, which enhances its effectiveness. It is innervated by the musculocutaneous nerve (C5–C7), which supplies the major flexors of the arm, including the biceps, brachialis, and coracobrachialis. While the brachialis also flexes the elbow, it is primarily innervated by the musculocutaneous nerve as well, and the option listing the radial nerve for its innervation is inaccurate. The triceps brachii extends the elbow, so it’s not the elbow flexor, and the axillary nerve does not innervate the biceps. Thus, the muscle acting as the prime mover for elbow flexion with its nerve supply is the biceps brachii (musculocutaneous nerve, C5–C7).