Which nerve is responsible for controlling muscle activity in the arm and hand?

The radial nerve is essential for controlling muscle activity in the arm and hand. It primarily innervates the muscles located in the posterior compartment of the arm and forearm, which are responsible for extending the elbow, wrist, and fingers. This nerve allows for functions such as gripping and holding objects, playing a critical role in hand coordination and strength.

While the median, ulnar, and musculocutaneous nerves also contribute to the function of the arm and hand, their roles are more specialized. The median nerve controls the muscles that allow for fine motor tasks and sensation in the thumb and first three fingers. The ulnar nerve is primarily responsible for the movement of the fingers and some hand muscles, especially those related to the little finger, and the musculocutaneous nerve mainly innervates muscles that flex the elbow. Thus, the radial nerve's widespread control over muscle extension in various parts of the arm and hand makes it the key player in overall muscle activity in these areas.