Blood-Brain Barrier

Neuron cells in the central nervous system (CNS)need to be protected against invasion, not only because infection might ensue, but also because their charge may be threatened by ionic compounds that exist in extracelluar space. Thus, cerebral blood vessels are unique in that they are highly restrictive to molecules that circulate in the blood.




The blood-brain barrier is formed by endothelial cells which are cemented together by specialized intercelluar structures called tight junctions. Small molecules such as oxygen (O2) are allowed to pass - and rightly so since of course the brain needs oxygen! What the brain doesn't need is irregular concentrations of ions like potassium or sodium which play a role in keeping cells polarized - readied for action potentials.