Multiple sclerosis. Coloured magnetic resonance imaging (MRI) scan of the brain of a ten year old girl suffering from multiple sclerosis (MS). In this horizontal (axial) section, the front of the brain is at top. MS is due to the destruction of the myelin sheaths around the axon nerve fibres of the brain and spinal cord, seen here as a large demyelinated lesion (pink, lower left). The brain's fluid-filled ventricles (upper centre) are pink. Axons in the affected area can no longer conduct nerve impulses, resulting in highly indiv- idual symptoms ranging from tingling to paralysis. MS is believed to be an autoimmune disorder in which the immune system attacks myelin.