Behavior and cognitive functions are results of a fine tuning of multiple neuronal synapsis and a myriad of biochemical reactions whose number, location, components, sequence, and logic are unknown.In entirely theoretical terms deleterious effects of reactive oxygen species (ROS) production during aerobic metabolism are neutralized by the antioxidant systems and in this manner the brain effectively regulates its oxygen consumption and redox generation capacity.The knowledge about the metabolic processes of the CNS is so elementary, so theoretical, that only in the previous paragraph we find two notable errors: aerobic metabolism and oxygen consumption.The phrase aerobic metabolism refers to the fact that the oxygen contained in any tissue of the human organism, such as the CNS, comes from the air that surrounds us, since it is supposedly absorbed through the lungs and reaches the bloodstream to be distributed to all the cells of the organism.However, since 1850 researchers of the stature of Christian Bohr, Carl Ludwig, and Halender, published works in which, according to their experiments, the diffusion of atmospheric oxygen through the pulmonary alveoli could not explain the enormous difference between the concentration of atmospheric oxygen, which ranges between 19 and 21%, and the % SpO 2 in the blood that reaches values of 98 and 99% [1].It was precisely the search for the mechanism that would explain such a difference between oxygen in the atmosphere and blood oxygen, which led these researchers to publish that there was no such thing, and that diffusion alone did not explain such a difference.Unfortunately, at that time, the work of Krogh appeared [2] who, by means of a theoretical mathematical model, apparently simple, explained the unlikely passage of atmospheric oxygen to the bloodstream through the pulmonary alveoli. Krogh's lung gas exchange model has been the foundation of respiratory physiology for the past 100 years even though the mathematical concepts it handles are so far-fetched that they cannot even be experimentally contrasted. PriMera Scientific Medicine and Public Health https://primerascientific.com/psmph The Central Nervous System and its Oxygen Content. Implications in the Context of Neurodegenerative Diseases 31Krogh's original model has been modified and something like 100 equations have been added to try to explain the supposed passage of atmospheric oxygen to the bloodstream through the pulmonary alveoli, but even so, the experimental results do not square with the predictions of such a model. So, research and care for patients during the past 100 years has been based on eminently theoretical models.So, returning to the phrase "aerobic metabolism of the CNS", we have the surprise that it is wrong because the oxygen we have inside the body does not come from the air that surrounds us but from the water that contains inside each cell that conforms us.