Which nerve innervates the supraspinatus muscle?

The suprascapular nerve is the nerve that innervates the supraspinatus muscle, making it the correct answer. This nerve arises from the brachial plexus, specifically from the upper trunk, and it plays a crucial role in shoulder movement. The supraspinatus muscle is one of the rotator cuff muscles, primarily responsible for initiating the abduction of the arm, particularly the first 15 degrees of shoulder movement. The proper functioning of the suprascapular nerve is essential for the action of the supraspinatus, as it provides the necessary motor signals to contract the muscle.

In contrast, the other options do not provide the appropriate innervation for the supraspinatus. While the medial nerve primarily innervates the forearm and hand muscles, the radial nerve innervates the posterior compartment of the arm and forearm, and the axillary nerve mainly innervates the deltoid and teres minor muscles. Each of these nerves serves different muscle groups and is not associated with the supraspinatus.