Schwann cells are the principle glia, which are neuron supports, in the peripheral nervous system. Schwann cells make up what is called the myelin sheath around the axon of the neuron. The function of this sheath is to protect and direct the nerve impulses.
If the Schwann cells are damaged it can cause a number of motor problems, which can include paralysis. If the myelin sheath that the Schwann cells make up becomes damaged then the impulses cannot flow properly, very much like the function of a coating on an electrical wire. The impulses are moved by an Na-K pump, which is a sodium potassium pump, that reverses the positive and negative charges along the sheath, forcing the impulses one way or the other. When a break occurs there is nothing there to reverse the charge along, causing the information not to be passed on to the brain.