While arteries are the main supply routes into the brain, blood ultimately delivers its payload of oxygen to its final destination via a vast web of smaller capillaries – or microvessels – which permeate brain tissue. The system that brings blood to the brain is akin to a road network that serves a city. Consequently, the circulatory system must be precisely tuned, constantly reacting to shifts in demand by diverting and increasing blood flow to where it is needed most. This is an important question because unlike other parts of the body, the brain resides in a confined space which restricts the amount of blood that is on hand at any given moment. What has not been fully understood is how the blood circulation system in the brain “knows” that it needs to ramp up blood flow to respond to the increased demand. Using imaging technologies, they have observed that when neurons start to fire there is an accompanying increase in blood flow to area of the brain that is active. Scientists have long understood that there is a direct correlation between brain activity and blood flow. In fact, the brain’s oxygen demands are enormous despite comprising only 2 percent of the body, our brains consume 20 percent of the body’s oxygen supply.

However, neurons only maintain a small reserve of energy and these cells require a continuous supply of oxygen, especially when the cells are firing and communicating with their neighbors. “This study demonstrates that microvessels in the brain play a key role in reacting to spikes in demand and accelerating the flow of blood to respond to neuronal activity.”Įnergy in the brain is generated almost exclusively from a form of metabolism that requires oxygen. “Our brains require a tremendous amount of energy and in order to meet this demand the flow of blood must be precisely choreographed to ensure that oxygen is being delivered where it is needed and when it is needed,” said Maiken Nedergaard, M.D., D.M.Sc., co-director of the University of Rochester Center for Translational Neuromedicine and lead author of the study. The findings could shed light on diseases like Alzheimer’s and help explain the cognitive decline that accompanies the disease. New research in the journal Neuron reveals how the brain is able to meet its massive energy demands with a “just in time” system that delivers oxygen that fuels nerve cells.

How many neurons in the brain