The brain and spinal cord make up the central nervous system (CNS). Nerves from the CNS extend throughout the body to make up the peripheral nervous system. Multiple sclerosis (MS) affects only the central nervous system.
The brain consists of two areas: a pair of hemispheres (on top) and the brainstem (on the bottom). Each hemisphere is divided into four lobes, each of which have special functions:
• Frontal lobes - planning, judgment, movement
• Temporal lobes - memory
• Parietal lobes - senses
• Occipital lobes - vision
• Limbic system - lies deep within the hemispheres, controls our emotions
The brainstem carries impulses from the hemispheres down to the nerves in the spinal cord, and from the spinal-cord nerves up to the hemispheres. The cerebellum, which controls balance and coordination, is located just behind the brainstem.
The body systems and multiple sclerosis
The nervous system:
Nerve messages to and from the brain travel along axons (nerve fibers) and are repeated in billions of locations within the nervous system. Think of it as billions of interconnected electrical wires creating a system of links.
Crucial in transmitting messages along the axons is a fatty protein called the myelin. Myelin is the insulation of the axons and allows messages to travel throughout the body. In MS, the myelin is damaged, and the damage—known as demyelination—causes the symptoms of MS. Not only is the myelin damaged, resulting in a loss of insulation, but the axon itself may be destroyed. Patches of myelin are replaced with scar tissue.
Without the myelin, signals transmitted throughout the nervous system are disrupted, or halted. The result is the brain's inability to send and receive messages.
The immune system:
Multiple sclerosis is thought to be an autoimmune disease in which the body's immune system mistakenly attacks normal tissues of the central nervous system. In MS, these attacks are aimed at the myelin. The end result of these attacks is the brain’s inability to send and receive messages.
The immune system does not attack all of the myelin at once; it only attacks it periodically. These periodic attacks vary in location and intensity and are very unpredictable; they also vary within a person and from one person to another.
The types of symptoms, severity, and the course of MS vary widely due to where the myelin is attacked and the extent of the attack.
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