Finger extension is primarily produced by which nerve and muscle?

• A. C7, C8, radial nerve - extensor digitorum
• B. C5, C6 - biceps
• C. C6, C7, C8 - extensor carpi radialis
• D. C8, T1 - abductor digiti minimi

Answer: (A)

Finger extension is driven mainly by the extensor digitorum, a major extensor in the posterior forearm. It straightens the fingers at the metacarpophalangeal joints, and its action is powered by the radial nerve, specifically via the posterior interosseous branch carrying motor fibers from spinal levels C7 and C8. This makes the combination of extensor digitorum with radial nerve input at C7–C8 the primary mechanism for extending the fingers.

Other options don’t fit as well: the biceps flexes the elbow and is innervated by the musculocutaneous nerve (C5–C7), not involved in finger extension; extensor carpi radialis mainly extends the wrist (not the fingers) and is also radial-innervated but not the primary finger extender; abductor digiti minimi is an intrinsic hand muscle innervated by the ulnar nerve, responsible for little finger abduction rather than finger extension.