What is the function of nodes of Ranvier in axons? In a neuroscience class I'm taking, it was explained that myelin covers axons in sections, the uncovered sections are called nodes of Ranvier, and signals propagate much faster in the covered sections. But if it is faster for signals to propagate along myelinated regions of the axon, why doesn't the entire axon get covered by myelin? Wouldn't that make it faster?

Every signal rapidly fades out with distance if it is not amplified. So if the whole axon were covered with myelin, action potentials wouldn't reach their target. Each Ranvier node can be seen as an active signal repeater.