Answer:
The blood-brain barrier prevents access of microbes in the blood from gaining access to the central nervous system.
Step-by-step explanation:
The Blood - Brain barrier -
The tissues present in the central nervous system have some extra protection , such that the unexposed blood or the immune system in the similar way as the other tissues . The blood vessels which supply the brain with the nutrients lies on the top of pia mater .
Now , due to this , the materials in the circulatory system have very limited ability to interact with central nervous system . This very process is called the blood - brain barrier .