Cage and oxygen

But nature is well taken care of, the person. Circulatory system, which provides oxygen to the brain, a very perfect. Suffice it to say that the total length of the finest vessels, capillaries that penetrate only one cubic centimeter of cortex, is a few hundred meters, and the total surface area of ​​the capillaries and red blood cells is several thousand times greater than the surface area of ​​the entire human body.

Virtually every major brain cells surrounded by several capillaries. However, despite the fact that the capillaries are visible over 300 years ago up to the last time was not known exactly how the bracing gas transferred to the cells from them. By analogy with the known mechanism of various substances in living organisms could be assumed that here the main role played by active electrical and chemical processes. But oxygen may be transmitted cells and much simpler by diffusion. This physical phenomenon lies in the mutual penetration of contacting substances is widespread in nature. Only if one is able to cope with the diffusion of performing such a difficult task?

Thus, the active electrochemical processes or passive diffusion? To answer the question, it was necessary to measure the concentration of oxygen in many points of the space between adjacent capillaries. However, the word "space" in this case sounds too loud. After one capillary from the other takes only a few hundredths of a millimeter.

Helped mathematics. On a sheet of paper depicted spatial model of the unit cell of the brain, consisting of a single nerve cell, surrounded by capillaries. Naturally, it had to make some simplifications. Real neuron presented in the form of a sphere with a diameter equal to the average size of a typical nerve cell, and fit it into a box whose edges were four "types" of the capillary. This mathematical model, despite its apparent schematic gave experimenters' unique method that will accurately, without errors to calculate the existing relationship between the capillaries and cells ».

And indeed, in the preparation of differential equations describing the behavior of the model are taken into account just received and previously known real physiological parameters of the human brain and mammals. It is guaranteed the accuracy of the simulation results.
Now the cell size is not important. It was only right to make and solve the system of equations. But this was not enough for some critical data. For example, it is unknown how much oxygen is consumed each nerve cell and the speed with which moves blood through the capillaries.

To find out, psychologists performed ingenious experiments. First experimental animals created an artificial circulation. The beating heart and the living brain connected plastic tube. She crashed into a special three-way valve, determine the amount of blood flowing in a certain area of ​​the cerebral cortex, and the number of oxygen contained therein. Then, the washed brain sacrificed animals using the same catheter for blood injected liquid dye. Dye penetrated only in that portion of the cortex, which is involved in the experiment. Colored tissue was excised and weighed. Thus experimenters find out how much oxygen consumes an average of every gram of bark.

But as you know, in the brain tissue itself nerve cells - neurons make up only a tenth of the volume, but the oxygen they consume many times more than the surrounding tissue-. Taking all this into account / it was easy to calculate the oxygen consumption of one neuron. As expected, this value was very high - several times the oxygen consumption and thus the energy cells of the heart muscle is working hard.

Modeling allowed to make absolutely clear conclusion: diffusion can successfully cope with the supply of oxygen to the brain cells.