Which intrinsic hand muscle is innervated by the ulnar nerve in addition to the other digits?

• A. Abductor pollicis brevis
• B. Flexor pollicis brevis (superficial head)
• C. Opponens pollicis
• D. Adductor pollicis

Answer: (D)

Understanding how intrinsic hand muscles are innervated clarifies grip and precision movements. The ulnar nerve handles most of the fine-tuning muscles that move digits other than the thumb, including the interossei between the fingers and the last two lumbricals. The thumb, however, has its own distinct innervation pattern.

The adductor pollicis is unique because it is the only intrinsic hand muscle that is innervated by the ulnar nerve. It acts to adduct the thumb, pulling it toward the palm, and it does so with two heads (transverse and oblique) attaching to the thumb’s metacarpal and proximal phalanx. The other intrinsic thenar muscles—the ones that move the thumb away from the palm or rotate it (abductor pollicis brevis, flexor pollicis brevis superficial head, and opponens pollicis)—are innervated by the median nerve. So, this muscle stands out as the ulnar-nerve–innervated intrinsic muscle that directly affects the thumb, while the rest of the intrinsic hand muscles involved with the digits 2–5 are supplied by the ulnar nerve for their actions.