Editing Haemodynamic response (section)

==Vascular anatomy overview==
In order to understand how blood is delivered to cranial tissues, it is important to understand the vascular anatomy of the space itself. Large cerebral arteries in the brain split into smaller [[arterioles]], also known as pial arteries. These consist of [[endothelial cells]] and [[smooth muscle|smooth muscle cells]], and as these pial arteries further branch and run deeper into the brain, they associate with glial cells, namely astrocytes. The intracerebral arterioles and [[capillaries]] are unlike systemic arterioles and capillaries in that they do not readily allow substances to diffuse through them; they are connected by [[Tight junction|tight junctions]] in order to form the [[blood brain barrier]] (BBB). Endothelial cells, smooth muscle, neurons, astrocytes, and pericytes work together in the brain order to maintain the BBB while still delivering nutrients to tissues and adjusting blood flow in the intracranial space to maintain [[homeostasis]]. As they work as a functional [[neurovascular unit]], alterations in their interactions at the cellular level can impair HR in the brain and lead to deviations in normal nervous function.<ref>{{cite journal | author = Iadecola Constantino | year = 2004 | title = Neurovascular Regulation in the Normal Brain and in Alzheimer's Disease | journal = Nature Reviews Neuroscience | volume = 5 | issue = 5| pages = 347–49 | doi=10.1038/nrn1387| pmid = 15100718 | s2cid = 36555564 }}</ref>