The cerebral vasculature originates from large arteries, such as middle cerebral artery and the circle of Willis. These arteries branch into the leptomeningeal arteries, which travel on the surface of the brain in the subarachnoid space. Leptomeningeal arteries further branch into smaller arteries and arterioles consisting of three layers: tunica intima (endothelium), tunica media (smooth muscle cells), and tunica adventitia (mainly collagen fibers). Finally, the terminals of arterioles become capillaries. Capillary lumen and brain parenchyma are separated by the BBB, which prevents the passive exchange of solutes between blood and brain (Iadecola, 2004).
