So special types of cells known as glial cells found inside the nervous system cover the axon of the neuron with a special insulating material known as the myelin. And this myelin or myelin sheath basically increases the speed at which our neuron propagates that action potential as we'll see in just a moment. So basically, our nervous system can be broken down into two categories. We have the central nervous system so that's the brain and the spinal cord and we also have our peripheral nervous system. And both of these categories contain their own glial cells. So schwann cells are the cells found in the peripheral nervous system while oligodendrocytes are those glial cells found in the central nervous system.