Life in the shadows

Actually, brain vessels do not live only in darkness. This life to the maximum isolation from the bad influences of any kind: a manual because the skull is a armor, which can be envied by any other authority, from chemical influences, because capillary network brain less permeable for larger molecules than other capillaries; fluctuations in blood almost no effect on brain activity due to the existence of the blood-brain barrier, open academician L.S. Shtern. Other agencies have also to some extent protected from the penetration of the fabric of garbage, but in the brain that is reserved especially strict. Finally, he is protected from gravity, as is floating in the liquid.
Cerebral circulation takes place in a hermetically closed, inextensible space. The expansion of some vessels should, therefore, to squeeze more. That's probably why there are a lot of large venous vessels: venous sinuses outside of the brain substance, venous plexus in the so-called ventricles of the brain floating in intraventricular liquid. The sudden expansion or extension of the arteries of the brain, therefore, will not cause compression of neurons, and will force the part of venous blood of these tanks in vecenane Vienna.
Brain shell richly supplied with blood and usneseni many receptors, which control the fluid in which it floats the brain and spinal cord.
If to tell about the blood circulation in the brain, most of all, probably, have to talk about the difficulties faced by psychologists in the study of this question. The brain does not tolerate artificial blood and vascular regulation cannot be investigated by the method of perfusion no animal blood donor, nor the blood of the animal, which put the experience. Therefore, measurement of blood flow in certain parts of the brain is extremely difficult, especially since the opening of the skull is pretty severe injury and may distort the result of experience. However, there is a lot of research carried out not only on animals, but even the human brain, of course, during the treatment of surgical intervention, accompanied by craniotomy. Are used and different indirect methods, such as radioisotope when harmless number labeled substances introduced into the blood, and then using a special counter determines the number of flying through the cerebral vessels particles. Use ultrasound.
In experiments on animals often use the introduction to the brain electrodes or even their implantation in order to judge about the functions of these parts of the brain and map this function with blood. Implanted micro-thermistors to determine the intensity of the circulation needed points of the brain changes in local temperature. Of course, it is much easier to install sensors pressure and blood flow in the carotid or vertebral arteries at their entrance into the cranial cavity, but it gives only a General result. In short, we should reckon with the fact that the brain-homeostatically body, and the trial itself must not violate the brain homeostasis.
In this respect, the brain is extremely finicky. It is understandable: remember the words of Barcroft about what to look intelligent in a changing environment - an idle exercise. The brain consumes oxygen more than any other tissue. Gray matter consumes about 20 % of the oxygen that is utilized by the body, with a weight of 0.8 % of total body weight, and some parts of the brain in a dozen times more keen to oxygen. During brain works increasing blood flow in 3-4 times and in the grey and white matter. Thus, the working hyperemia brain tissue is not particularly great, but alone the huge flow.
Since maintaining a constant internal environment for the brain is more important than to any body, one would assume that his vessels are closely connected with vasomotor center and richly innervated. But it is not! Well stocked nerve endings only large vessels outside of the brain, and the small arteries and arterioles have extremely sparse number of efferent nerve fibers. Prekapilliarny sphincter is not here. This sybaritic, you see, little one only independence from chemical and mechanical influences. He does not want to depend at all on the system of regulation of blood flow.

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