What is Blood–brain barrier?
[[File:10.1371 journal.pbio.0050169.g001-O.jpg|250px|right|thumb|Part of a network of [[capillary|capillaries]] supplying [[brain cell]]s]] The '''blood–brain barrier''' ('''BBB''') is a highly selective [[wikt:permeability|permeability]] barrier. It controls what gets from the [[bloodstream]] into the [[brain]], and what does not. For example, things that the brain needs to survive (water, [[glucose]], and [[Amino acid|amino acids]]) can get through the barrier. However, the barrier stops many harmful things, like [[bacteria]] and [[Virus|viruses]], from getting into the brain. This helps protect the brain from getting an [[infection]]. The blood-brain barrier is formed by [[capillary]] [[endothelium|endothelial]] cells.<ref>{{cite journal | url=http://pharmrev.aspetjournals.org/content/49/2/143 | title=The blood-brain barrier in neuroinflammatory diseases | author=de Vries, Helga E. |display-authors = etal | journal=Pharmacological Reviews| year=1997 | volume=49 | issue=2 | pages=143–156 | pmid=9228664}}</ref> It allows the passage of water, some gases, and [[lipid]]-soluble molecules by passive diffusion. It also allows the selective transport of molecules such as [[glucose]] and [[amino acids]] which are crucial to [[nerve]] function.<ref>{{cite web| title = About| work = Blood brain barrier| access-date = 7 May 2013| url = http://bloodbrainbarrier.jhu.edu/about/|publisher=Johns Hopkins University}}</ref> On the other hand, the blood-brain barrier may prevent the entry of [[neurotoxin]]s by means of an [[active transport]] mechanism. A few small areas in the brain do not have a blood-brain barrier. == Discovery == [[Paul Ehrlich]], a [[Germany|German]] [[Medical doctor|doctor]], discovered the blood-brain barrier. He [[Injection|injected]] [[dye]] into [[mice]]'s bloodstreams. The dye got to every [[Organ (anatomy)|organ]] except the brain. The blood-brain barrier had stopped the dye from getting through to the brain. Then one of Ehrlich's students injected the dye right into the [[Lab mice|mice