What mechanism involve in multiple sclerosis?

Hi Maria, It is theorized that the immune system is attacking the myelin sheath which protects the nerves. As a consequence the body's communication system is disrupted since the nerves conduct messages to and from the brain. Researchers think that a person must be genetically predisposed to the disease, and in addition to that, they must also come into contact with something in the environment to get MS. The disease is not fatal since it does not attack the vital organs, and it is also not always degenerative. I have had MS for 20 years. Many, many people with MS lead normal lives and have a normal life span. For accurate information contact the National MS Society (nmss.org) This is the last place you will get accurate information.

MS is caused by degeneration of the myelin sheath that surrounds a nerve. It's almost like losing the covering around a wire. As a result, the conduction does not occur as readily and depending on where it is affecting, depends on a person's signs and symptoms.

Whilst answerer nr1 is correct let me elaborate a bit as he assumes you are familiar with a lot of things. Lets compare the spinal cord with a telephone cable insulated with a PVC sheath. The cable is transmitting the neural impulses coming from the brain (motoric impulses) (= orders to the various muscles to move) and the sensorial impulses (impulses from the various senses). At a certain moment in time (nobody knows why (it may have something to do with the immune system of the body, like the body misreading its ADN and attacking itself) the myelin, (the PVC around the cable) gets infected . After some time the infection abates and te disease goes into remission. However on the spot of the infection the myelin has been destroyed and is not replaced. A scar is left (sclerum).
After some months a new similar episode may occur on the same place or on another (Multiple sclera). If the myelin is completely destroyed at some place, the motoric nerves leaving the cord do not receive any impulses any more and the relative muscles do not receive any commands. The patient therefore can present symptoms like difficulty in walking, in standing up etc, all depending on the location of the sclera. The disease develops over years with periods of months of remissions but always downhill. Eventually the patient will pass away if one of his/her main systems is affected.