What is multiple sclerosis?

MS is a chronic neurological condition that affects the central nervous system, which is comprised of the brain and spinal cord. In the CNS, nerve fibers (called axons) are protected by a fatty layer of insulation called myelin. Myelin allows nerve signals to travel properly. 

In MS, overactive immune cells cause inflammation, which damages the myelin. This results in a loss of myelin – called demyelination – and some degree of axonal damage. Wherever the myelin is destroyed, a damaged area of white matter known as a lesion (or plaque) will occur. Over time, hardened scar tissue develops at the lesion site. This hardened scar tissue, or sclerosis, may develop at multiple sites throughout the CNS, hence the name multiple sclerosis. This scarring disrupts the transmission of nerve signals that communicate a desired action from the brain, through the spinal cord, to various parts of the body.

A simple illustration

Imagine this: you disconnect your cell phone from its charger as you get ready for a busy day. But even though it has been connected all night, you notice the battery is only partially charged. You look at the cord and notice a spot where the insulation has been stripped away and the wires inside are exposed. Because the path by which the current travels is damaged, not all of the electricity sent from the outlet reached its target, your phone. 

This analogy is helpful in understanding MS. When signals from the brain travel along nerves where the insulation has been damaged or lost, those signals may be interrupted or distorted, producing the many symptoms associated with MS.