Multiple sclerosis. Coloured Magnetic Resonance Imaging (MRI) scan of the brain of a patient suffering from multiple sclerosis (MS). In this horizontal slice through the brain, the two cere- bral hemispheres are seen: the outer grey matter is coloured brown; inner white matter is yellow. Demyelinating lesions, due to the destruction of the myelin sheath around the axons of nerve cells in multiple sclerosis, appear as two bright red circular regions. As such patches of myelin in the brain and spinal cord are destroyed in this disease, a range of symptoms result including: unsteady gait, tremors, involuntary eye movements and speech defects.