I disagree with the term 'more advanced', but there is a huge difference between the invertebrate and vertebrate nervous systems: we have myelin, which insulate

I disagree with the term 'more advanced', but there is a huge difference between the invertebrate and vertebrate nervous systems: we have myelin, which insulates the axons and allows signals to travel many times faster. Without myelin, large bodies with centralized nervous systems are not possible. To illustrate the difference, take an example of stubbing your toe. It's a good example because it's unexpected, sudden and originates at the furthest point in your body away from the brain. When you stub your toe, you feel two waves of pain. The first arrives quickly, within about a tenth of a second, and is a sharp stabbing pain. That signal travels by the A-delta fibres, which are myelinated and have a conduction speed of 2 to 30 m/s. The second wave is delayed by 1-2 seconds and is a dull sort of pain. That signal is conveyed by the C fibres, which are unmyelinated and have a conduction speed of <2 m/s. If we did not have myelin, all of the signals to and from the extremities would be similarly delayed. It would be impossible to respond to stimulus or coordinate whole-body actions like walking.