The ulnar nerve is one of the major nerves of the upper extremity. Nerves are structures that allow information to travel from the brain to the periphery of your body, and nerves can also send messages back to the brain. Nerves in the upper extremity carry important information about sensations that you can feel, and movements that your brain wants your body to make.
When nerve function is impaired, people may experience symptoms of pain, weakness, and abnormal sensation.
Source: Verywell Health