College of Massage Therapists of British Columbia (CMTBC) Practice Exam

Which muscle is responsible for abducting the index finger?

1. 1st dorsal interossei

2. Abductor pollicis longus

3. Flexor digitorum superficialis

4. Palmaris longus

The correct answer is: 1st dorsal interossei

The muscle that is responsible for abducting the index finger is indeed the 1st dorsal interossei. This muscle is located in the hand and plays a crucial role in the movement of the fingers. Specifically, the dorsal interossei muscles, which include four individual muscles, are responsible for the abduction of fingers away from the midline of the hand, which in this case includes the index finger. The 1st dorsal interossei originates from the adjacent sides of the metacarpal bones of the index and middle fingers and inserts into the proximal phalanx and extensor expansion of the index finger. When this muscle contracts, it pulls the index finger away from the middle finger, effectively performing abduction. Other options listed pertain to different functions: the abductor pollicis longus primarily abducts the thumb, the flexor digitorum superficialis flexes the fingers at the proximal interphalangeal joints, and the palmaris longus primarily acts to flex the wrist. Thus, the specific action of finger abduction, particularly for the index finger, is correctly attributed to the 1st dorsal interossei.