Question

why is brain contained in a fluid filled balloon​

Answer 1

Inside the brain there is a fluid called cerebrospinal fluid which prevent the brain from getting mechanical shocks by reducing friction.

Answer 2

The fluid is called cerebro-spinal fluid.

It protects the brain from sudden shocks.

Brain is protected by cranium and spinal cord is protected by vertebral column.                                                                                                                   The two types of nerves:-

1) cranial nerves

2) spinal nerves