We have the central nervous system or the CNS and the peripheral nervous system or the PNS. Now, the central nervous system consists of the brain and the spinal cord. And the only type of neurons found in the central nervous system are internal neurons. Now, on the other hand, the peripheral nervous system consists of everything else, of everything outside of the brain and the spinal cord and it does not contain any interneurons. The only type of neurons this system contains are motor neurons and sensory neurons. And we'll see what those are in just a moment.