Research into multiple sclerosis, illustration. At upper left is a healthy neuron and its axon and the axon's intact myelin sheath (red), with its supporting microglial cells. At lower right is a neuron with damaged myelin (red) on its axon, caused by white blood cells (yellow) attacking the myelin. It is this autoimmune response and damage that causes neurodegenerative diseases such as multiple sclerosis. Axons in the affected area can no longer conduct nerve impulses, resulting in symptoms ranging from tingling to paralysis. This is caused by neuronal degradation and a gradual loss of nerve function.