Abstract
The blood-brain barrier (BBB) is the anatomophysiological unit that interfaces between the blood and the brain. It is composed of brain vascular endothelial cells and their surrounding astrocytes and pericytes. These cells interface with neurons to form a functional unit that regulates blood flow in the brain and the traffic of substances between blood and brain parenchyma. The proper function of the BBB requires specialized roles for each of the cell types that compose it; thus, the endothelial cells form a proper biological barrier by expressing tight junctions (TJ) that seal the intercellular space while forming paracellular ion pores. The expression of TJ brings an additional benefit to the endothelial cells as they are determinants of membrane polarization; the resulting cell polarity is crucial for the proper expression of membrane transporters and ion channels responsible for the transcellular exchange of substances across the endothelium. The physiological properties of endothelial cells, however, are regulated by their interaction with astrocytes and pericytes that in turn interact with each other and nearby neurons. This chapter explores the cellular structure of the blood-brain barrier and provides an introduction to the molecular characteristics of tight junctions and electrophysiological properties of the brain vascular endothelium.