Now of course, because the size of our body is limited, that means the length and the thickness of that axon is also limited. That is, we cannot actually make our axon too thick or too short or too long. Now, instead of actually increasing the area or increasing the area or decreasing the length of the axon, the way that our body increases the speed at which our action potential moves along the axon is by using a special type of insulating material. 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.