A central nervous system is made-up of brain and spinal cord.
Brain is a delicate organ and it is an important organ for a variety of activity, therefore, it needs to be carefully protected. Brain is protected in a bony box called cranium. Inside the bony box, the brain is covered by meninges. Fluid between the meninges protects brain by shock absorption.
Spinal cord is protected in a hard skeletal structure called vertebral column or backbone.