What four structures protect the central nervous system?
The brain is protected by the skull (cranium), cerebrospinal fluid and 3 protective membranes (Meninges).
The spinal cord is protected similarly but with vertebrae instead of the cranium.
The brain is first protected by the skull (cranium). This offers physical protection and so naturally is one of the hardest bones in the body. The skull acts like a helmet for your brain, and helps to prevent damage from mechanical stress (things like knocks and falls).
The spinal cord is also surrounded by some very hard bone, but this time it comes in the form of the vertebrae.
Next, we have the three protective membranes - the meninges. These are made out of connective tissue and provide a cushioning from the hard skull of the brain, jolting against the vertabrael column (in the spinal cord) or from any damaging impacts.
The three meninges are the Dura Mater (outer), The Arachnoid (middle) and the Pia Mater (inner).
You could remember this order with some sort of mnemonic or story such as - Dur-ing (Dura Mater)the invasion of the Arachn-ids (arachnoid), Pia-nos (Pia Mater) were very rare.
Finally, there is a special fluid, called cerebrospinal (cerebro for brain, spinal for the spinal cord) that circulates the entire central nervous system. It occupies the space between the Pia Mater and Arachnoid and supplies nutrients (like blood in the rest of the body), disposes of waste and acts as a shock absorber (which is why I've included it as a protective structure)
I hope this helped; let me know if I can do anything else:)