Haemodynamic response

Haemodynamic response

Haemodynamics is a medical term for the dynamic regulation of the blood flow in the brain. It is the principle on which functional magnetic resonance imaging is based.

Neurons, like all other cells, require energy to function. This energy is supplied in the form of glucose and oxygen (the oxygen being carried in haemoglobin). The blood supply of the brain is dynamically regulated to give active neural assemblies more energy whilst inactive assemblies receive less energy [cite book
last = Siesjo
first = Bo K.
authorlink = Bo K. Siesjo
title = Brain Energy Metabolism
publisher = Wiley
date = 1978
location = New York
pages = 612
id = 0 471 99515 0 ] .

Molecular biology of hemodynamic regulation

The precise mechanism behind neurovascular coupling is currently under active research and furious debate, but roughly the following model has gained consensus:
# Active excitatory neurons release the neurotransmitter glutamate
# Glutamate opens NMDA receptors on other neurons which allows calcium ions into the neuron
## Calcium activates nitric oxide synthase which produces nitric oxide
## Nitric oxide diffuses out and dilates smooth muscle surrounding local arterioles
## This dilation allows more blood into the local capillaries
## Hence more oxygen and glucose reaches the neurons [cite journal
last = Stefanovic
first = Bojano J.
authorlink = David J Rossi
coauthors = Wolfram Schwindt, Mathias Hoehn and Afonso C Silva
title = Functional uncoupling of hemodynamic from neuronal response by inhibition of neuronal nitric oxide synthase
journal = Journal of Cerebral Blood Flow & Metabolism
volume = 27
pages = 741–754
date = 2007
url = http://www.nature.com/jcbfm/journal/v27/n4/full/9600377a.html
doi = 10.1038/sj.jcbfm.9600377
accessdate = 2007-05-22 ]
# Glutamate also binds to the metabotropic glutamate receptor on astrocytes
## This allow calcium into the astrocyte
## Which activates phospholipase A2 (PLA2)
## Which produces arachidonic acid (AA)
## Which is converted by cyclo-oxygenase
## Into PGE2 and released through the astrocytic endfeet
## Which dilates local smooth muscle and allows greater blood flow [cite journal
last = Rossi
first = David J
authorlink = David J Rossi
title = Another BOLD role for astrocytes: coupling blood flow to neural activity
journal = Nature Neuroscience
volume = 9
pages = 159–161
date = 2006
url = http://www.nature.com/neuro/journal/v9/n2/full/nn0206-159.html
doi = 10.1038/nn0206-159
accessdate = 2007-05-22 ]

References

External links

* [http://www.loni.ucla.edu/SVG/index.php?vid=261 An animation of neurovascular coupling]


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