Nerve fibers (axons) coming from neurons and going to other neurons are surrounded by myelin. The axons and the myelin that cover them make up the white matter. Myelin insulates the nerve fibers just like insulation on copper wires. This insulation is important because it speeds up the communication between different areas of the brain. Myelin allows a signal to travel the length of a football field in one second.
The plaques of inflammation are areas of damage to myelin and therefore interfere with the function of axons to send messages. Although symptoms of MS will depend on the location of the plaque, many plaques in the brain will not cause any obvious neurologic symptoms.