The barriers within the blood vessels of the brain serve to protect neurons by:

• excluding, effluxing and metabolizing neurotransmitters and potential neurotoxic compounds (including plasma proteins, antibodies, drugs) from blood and brain
• safeguarding the delicate ion balances around neurons in the brain
• preventing immune cells, bacteria or viruses from entering the brain

This so-called blood-brain barrier, or BBB, is characterized by a uniquely specialized tight endothelial cell layer that covers the smallest blood vessels (capillaries) in the brain.