Multiple sclerosis. Coloured magnetic resonance imaging (MRI) scan of the brain of a patient who is suffering from multiple sclerosis (MS). The front of the brain is at top in this horizontal (axial) section. MS is due to the destruction of the myelin sheaths around the axon nerve fibres of the brain and spinal cord. This is seen in the several large demyelinated lesions (black/orange). The brain's healthy fluid-filled ventricles (upper centre) are black. Axons in the affected area can no longer conduct nerve impulses, resulting in symptoms ranging from tingling to paralysis. MS is believed to be an autoimmune disorder in which the immune system attacks myelin.