Credit: JOHN ZAJICEK / SCIENCE PHOTO LIBRARY Caption: Multiple sclerosis. Coloured scanning electron micrograph (SEM) of microglial cells (round) ingesting oligodendrocytes (branched). This is the process thought to occur in multiple sclerosis (MS). Oligodendrocytes form insulating myelin sheaths around nerve axons in the central nervous system. Microglia normally ingest cell debris and bacteria as part of the body’s immune response. In MS they attack oligodendrocytes, possibly triggered by a virus in people with hereditary susceptibility. Destruction of myelin sheaths leads to loss of nerve function. Symptoms include unsteady gait, visual and speech defects, and paralysis. Magnifi cation: x670 when 10cm wide.