Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Multiple Sclerosis ?
    ### Response:
    Multiple sclerosis (MS) is a nervous system disease that affects your brain and spinal cord. It damages the myelin sheath, the material that surrounds and protects your nerve cells. This damage slows down or blocks messages between your brain and your body, leading to the symptoms of MS.
    