While most everyone has heard of MS, you certainly wouldn't be the first person to lack a full understanding of its nuts and bolts. When MS is suspected or diagnosed, it is not uncommon for someone to ask “What exactly is MS?”

MS is defined as a chronic, inflammatory, demyelinating disease that affects the central nervous system (CNS). What that means in a nutshell is this: MS is thought to be an autoimmune disease that affects the command center of your body's functions — your CNS — resulting in a myriad of neurological symptoms. To get a better handle on the mechanics of MS, you must first understand the roles the CNS and the immune system play.

The Nervous System

The nervous system is composed of two parts:

• The central nervous system is made up of the brain, spinal cord, and optic nerves. It interprets sensory information and sends commands to the muscles.

• The peripheral nervous system (PNS) connects the CNS to the glands, sensory organs, and muscles through a branching network of nerves.

Both the CNS and the PNS are made up of nerves that act as the body's messenger system. Each nerve is covered by a fatty substance called myelin, which provides insulation and helps in the transmission of nerve impulses, or messages between the brain and other parts of the body. MS is exclusive — its sole target is the CNS.