If median nerve is injured at the wrist, then loss of function of all of the following muscles will take place, EXCEPT?
The median nerve supplies several muscles in the forearm and hand. In the forearm, it innervates the pronator teres, flexor carpi radialis, palmaris longus, and the flexor digitorum superficialis. In the hand, it innervates the thenar muscles (opponens pollicis, abductor pollicis brevis, flexor pollicis brevis), and the first and second lumbricals. Also, the median nerve provides sensory innervation to the palmar side of the thumb, index, middle finger, and half of the ring finger.
If the injury is at the wrist, distal to the origin of the thenar muscles, then the thenar muscles might still be intact if the nerve is injured after the branches to those muscles have already been given off. Wait, where does the median nerve branch to the thenar muscles? The recurrent branch of the median nerve supplies the thenar muscles. If the injury is at the wrist, like in the carpal tunnel, the recurrent branch is already proximal. So if the injury is at the wrist, the thenar muscles would still be innervated. Therefore, the muscles affected would be the flexor digitorum superficialis, pronator teres, flexor carpi radialis, and palmaris longus in the forearm, and the first and second lumbricals in the hand. The thenar muscles (opponens, abductor, flexor pollicis brevis) are spared because they are innervated by the recurrent branch, which is proximal to the wrist.
So the question is asking which muscle is NOT affected. The options might include muscles like flexor digitorum superficialis, pronator teres, palmaris longus, and thenar muscles. The correct answer would be the thenar muscles, as they are not affected by a wrist injury. Wait, but if the injury is at the wrist, and the recurrent branch is already given off before, then the thenar muscles are still working. Therefore, the exception would be one of the thenar muscles. So the answer would be the thenar muscles, like abductor pollicis brevis or opposens pollicis. Therefore, the correct answer is the one that is a thenar muscle.
**Core Concept** The median nerve innervates forearm flexors and thenar muscles. Injury at the wrist (distal to the origin of the thenar motor branch) spares the thenar muscles, which are supplied by the **recurrent branch** of the median nerve, a proximal branch.
**Why the Correct Answer is Right** The **thenar muscles** (opponens pollicis, abductor pollicis brevis, flexor pollicis brevis) are innervated by the **median nerve’s recurrent branch**, which arises **proximal to the wrist**. A wrist injury cannot damage this proximal branch, so these muscles remain functional. Other median nerve branches (e.g., to flexor digitorum superficialis, pronator teres) are affected because they originate distal to the injury