In MS, these attacks are aimed at the brain and spinal cord, or the central nervous system. The central nervous system is made up of nerves that act as the body's messenger system. Each nerve is covered by a fatty substance called myelin, which insulates the nerves and helps in the transmission of nerve impulses, or messages between the brain and other parts of the body.
Plaques form when the protective myelin sheath is destroyed, a process called demyelination.
Without the myelin, signals transmitted throughout the central nervous system are disrupted or halted. The brain then becomes unable to send and receive messages. Although the nerves can regain myelin, this process is not fast enough to outpace the deterioration that occurs. The types of symptoms, severity of symptoms, and the course of MS vary widely, partly due to the location of the scar tissue and the extent of demyelination. While symptoms show up in the central nervous system, MS appears to be the result of problems in the immune system.