The radial nerve is a major nerve in the upper limb that originates from the brachial plexus. It primarily innervates the muscles in the posterior compartment of the arm and forearm, allowing for movements such as extending the elbow, wrist, and fingers. In addition to motor functions, the radial nerve also provides sensory innervation to parts of the hand and forearm. Damage to the radial nerve can lead to conditions like wrist drop, where a person is unable to extend their wrist and fingers, affecting hand function.