This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Median nerve injury at wrist, is commonly tested by: 
Select and explain. 
A. Contraction of abductor pollicis brevis, B. Contraction of flexor pollicis brevis, C. Loss of sensation on palm, D. Loss of sensation on ring finger
A: Contraction of abductor pollicis brevis
Answer: A: Contraction of abductor pollicis brevis 
Explanation: Injury or compression of median nerve at wrist (eg carpel tunnel syndrome) can be tested by 1. Pen test for loss of action of Abductor pollicis brevis 2. Ape thumb deformity Q (adducted posture of thumb) 3. Loss of opposition & abduction of thumb Q (d/ t wasting of thenar muscles) 4. Sensory loss - lateral 31/2 of digits & 2/3 palm (autonomous zone is tip of index & tniddle finger) Abductor pollicis longus is supplied by posterior interosseous nerve (br. of radial nerve)Q; so abduction of thumb is not completely lost.