Metabolic Demands of The Human Brain
The brain is dependent on a constant supply of glucose as it doesn’t have any storage capacity in itself to store glucose as glucagon. In addition to this, the brain doesn’t use alternative sources of fuel such as fatty acids which is believed to be due to an evolutionary protective mechanism from the harmful effects of fatty acid oxidation. Thus, due to its reliance on glucose for fuel the brain can only derive its energy via aerobic glycolysis and oxidative phosphorylation. Although it can also use ketone bodies, this fuel source is limited and not as efficient as glucose.
The brain is a highly heterogeneous organ in terms of its functions and cell type. Different nerve cells have a variety of functions and thus a variable demand for energy. More than 20% of the body’s energy is consumed by the brain although it accounts for less than 2% of the total body mass. This energy as stated above is produced by aerobic glycolysis which is dependent on oxygen, therefore, oxygen levels are a significant factor that influences brain cells’ functionality. Despite a large number of studies conducted on understanding the metabolic processes of the brain, the amount of oxygen consumption by the brain has not been known until now.
LMU Neurobiologists Make A Breakthrough
Neurobiologists from LMU have recently calculated the amount of oxygen the human brain consumes based on the activity of some nerve cells. For the first time in the history of medical science, neurobiologists Hans Straka, Suzan Özugur, and Lars Kunz have discovered a method to directly measure the oxygen consumed by the brain by correlating it with the neural cell functions.
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Using electrochemical sensors in tadpoles, the neuroscientists determined the concentration of oxygen in the brain. This technique enabled them to control the oxygen levels within the brain while simultaneously inhibiting brain function by controlling nerve cell functional activity using pharmacological inhibitors of neurotransmitters. By examining eye movements while controlling nerve cell activity, the neurobiologists analyzed the association of nerve cell function with oxygen consumption.
“We have found that the brain is anoxic in a normal air-saturated environment, which means that no oxygen can be measured,” said Straka.
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Any oxygen consumed by the nerve cells is immediately utilized for aerobic glycolysis for energy. However, if oxygen saturation levels of the atmosphere were twice the normal concentration, the utilization of oxygen for energy was saturated creating an abundance of oxygen within the brain. For nerve cell activity, only half of the oxygen was used while the remaining half was required by glial cells to maintain the basic metabolic rate of both glial cells and nerve cells. But in situations of increased brain activity, more oxygen was utilized for nerve cell activity than basic metabolic rate.
Understanding the influence of oxygen saturation or deficiency on brain activity is a crucial step to further research the mechanism by which our brain processes information.