What is the name of the protective blood–brain barrier in the human nervous system?

The blood–brain barrier is the protective barrier that regulates movement between blood and nervous tissue.

It is formed mainly by specialized endothelial cells lining the tiny blood vessels of the brain. These cells are joined by unusually tight junctions, which restrict the passage of many substances. Support from pericytes, astrocytes, and the surrounding extracellular environment helps maintain the barrier’s properties.

The barrier allows essential materials such as oxygen, glucose, and certain nutrients to reach brain cells while limiting many toxins, pathogens, and rapid chemical fluctuations. Some molecules cross through transport proteins, and small lipid-soluble substances can pass more readily than large or water-soluble molecules.

The blood–brain barrier is selective rather than absolutely sealed. Certain brain regions have more permeable capillaries, and inflammation, tumors, infection, trauma, or stroke can disrupt barrier function. Its selectivity is also a challenge in medicine because many potentially useful drugs cannot easily enter the brain. The term is usually written with an en dash: blood–brain barrier.