Basically, CNS refers to the Central Nervous System. That includes the brain and the spinal cord. PNS refers to the Peripheral Nervous System. That includes any nerve outside the CNS such as nerves in our arms, hands, legs, feet, and other areas of the body. This is just basic, there's a lot more to both systems. If you google in either of them I'm sure you can get much more detailed information. If you wait, maybe a more knowledgeable and/or has-the-time-to-do-the-research blurter will help you out more. Hope this helps.