Unmyelinated refers to nerve fibers that lack a protective covering called myelin. Myelin is a fatty substance that insulates nerve fibers, allowing electrical signals to travel quickly. In unmyelinated fibers, the signals move more slowly, which can affect how quickly information is transmitted in the nervous system. These unmyelinated fibers are often found in areas where slower signal transmission is acceptable, such as in certain types of pain sensation. They play a crucial role in the nervous system, helping to relay information about temperature and pain to the brain.