The radial nerve is a major nerve in the upper limb that originates from the brachial plexus, specifically from the spinal nerves C5 to T1. It travels down the arm and is responsible for controlling the muscles that extend the elbow, wrist, and fingers. It also provides sensation to parts of the arm and hand. Injury to the radial nerve can lead to conditions such as wrist drop, where a person is unable to extend their wrist and fingers. This nerve is crucial for hand function and is often assessed in cases of arm trauma or nerve compression.