The central nervous system is surrounded by cerebrospinal fluid. This fluid acts to cushion and protect the central nervous system when you move around. Even more protection is given by the meninges, which are the membranes that cover the brain and spinal cord.
The meninges are composed of three layers of membranes enclosing the brain and spinal cord.
• Pia mater – The inner layer. It is like tissue paper that closely adheres to the brain and spinal cord, dipping into the various folds and crevices.
• Arachnoid mater – The middle layer. It is a filmy membrane that is joined to the inner layer (Pia mater) by fine threads resembling a cobweb.
• The dura mater- The outer layer. It is a parchment-like membrane, and adheres to the skull and spinal canal.
The cerebral spinal fluid (CSF) is the fluid that circulates in the spaces in and around the brain and spinal cord.
Meningitis is a serious inflammation of the meninges, affecting the delicate membranes covering the brain and spinal cord.
It is almost always caused by an infection, usually by the entry of a microorganism such as a bacterium (bacterial meningitis) or a virus, from an infection somewhere else in the body (viral meningitis). In rare cases it can be triggered by a fungus or parasite.
The microorganisms travel through the blood and into the meninges and cerebral spinal fluid.

In the bloodstream, infection-causing microorganisms are fought off by white blood cells, an important part of the immune system. However, there are no white blood cells in the cerebral spinal fluid to fight infectious agents.
Once infectious organisms have entered the cerebrospinal fluid, the body's defence cannot control their rapid growth and the disease races through the delicate surfaces and fluids of the central nervous system.
As the immune system gears up to fight off the microorganisms, it sends out chemical signals that produce inflammation and interfere with the normal functioning of the central nervous...