The neurovascular unit (NVU) is a group of closely related cells and extracellular matrix components that function in the homeostatic

haemodynamic response In haemodynamics, the body must respond to physical activities, external temperature, and other factors by homeostatically adjusting its blood flow to deliver nutrients such as oxygen and glucose to stressed tissues and allow them to function. ...

of cerebral

hyperaemia Hyperaemia (also hyperemia) is the increase of blood flow to different tissues in the body. It can have medical implications but is also a regulatory response, allowing change in blood supply to different tissues through vasodilation. Clinically, ...

. Cerebral hyperaemia is a fundamental central nervous system mechanism of homeostasis that increases blood supply to neural tissue when necessary. This mechanism controls oxygen and nutrient levels using the methods of

vasodilation Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction, ...

and

vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessel ...

in a multidimensional process involving the many cells of the neurovascular unit. The cells of the NVU sense the neural needs of oxygen and glucose and trigger the appropriate vasodilatory or vasoconstrictive responses. Thus the NVU plays a vital role of neurovascular coupling of neural activity and

cerebral blood flow Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arterie ...

Imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

has shown that areas of neural activity in the brain are supplied with an increased blood flow while blood flow to inactive regions is restricted. Dysfunction of the NVU has been seen to be associated with

neurodegenerative disease A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic ...

s. However, the mechanisms are not well understood. One factor may be related to

astrocyte Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of e ...

dysfunction.

Function

Cells of the neurovascular unit include

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s, blood-brain-barrier

epithelial cells Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

myocyte A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

s and

pericyte Pericytes (previously known as Rouget cells) are multi-functional mural cells of the microcirculation that wrap around the endothelial cells that line the capillaries throughout the body. Pericytes are embedded in the basement membrane of blood ca ...

s. Other components come from the

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...

. The brain has a very high energy need and no storage support which means that it has to take oxygen and glucose from the dynamic blood supply. Imaging has shown that areas of brain activity are supplied with an increased flow of blood. The cells of the NVU sense the needs of neural tissue and release many different mediators that engage in signaling pathways, and effector systems such as the myogenic effect; these mediators trigger the

vascular smooth muscle cells Vascular smooth muscle is the type of smooth muscle that makes up most of the walls of blood vessels. Structure Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood ve ...

to increase blood flow through vasodilation or to reduce blood flow by vasoconstriction. This is recognized as a multidimensional response that is acknowledged to operate across the cerebrovascular network as a whole.

Clinical significance

The NVU concept with its involvement with neurology was made formal in the

NINDS The National Institute of Neurological Disorders and Stroke (NINDS) is a part of the U.S. National Institutes of Health (NIH). It conducts and funds research on brain and nervous system disorders and has a budget of just over US$2.03 billion. The ...

''Stroke Progress Review Group'' in 2001. Dysfunction in the NVU is associated with neurodegenerative diseases including

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

, and

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unst ...

though its mechanism is not well understood. However, it is recognised that maintaining the health of the cerebrovascular system promotes good health for the brain.

References

{{Reflist Neurology