Blood supply to the brain occurs through the vertebral and internal carotid arteries (Fig.). The vertebral arteries are connected at the rear edge of the main artery.
| Diagram of the brain base arteries: |
1 — front connecting;
2 - anterior cerebral;
3 - internal sleepy;
4 - middle cerebral;
5 - anterior artery of the choroid plexus;
6 - rear connective;
7 - posterior cerebral;
8 - superior cerebellar;
9 - the main;
10 — artery of the labyrinth;
11 — anterior lower cerebellar;
12 - vertebrate;
13 - posterior lower cerebellar;
14 - posterior and 15 - anterior spinal arteries.
At the front edge of the bridge, the main artery divides into two posterior cerebral arteries, connecting the posterior communicating arteries with the internal carotid artery. The middle and anterior cerebral arteries depart from the latter. The anterior cerebral arteries are interconnected by the anterior communicating artery. The ring formed by arteries on the basis of the brain is called the arterial (Willisian) circle. The medulla oblongata and the bridge are supplied with the branches of the anterior spinal and vertebral arteries, the midbrain with the branches of the posterior cerebral arteries. The latter also nourish the occipital lobe and the lower part of the temporal lobe of the brain. The anterior cerebral artery supplies the basal part of the frontal lobe, as well as the medial surface of the frontal and parietal lobes and most of the corpus callosum. The middle cerebral artery passes on the basis of the brain; in the area of the anterior perforated space, a number of piercing branches penetrate the substance of the brain and supply the subcortical nuclei. Then it lies in the lateral groove and feeds the outer surface of the hemisphere.Go
The venous system of the brain is represented by superficial veins lying in the pia mater and deep, leading to blood from the subcortical structures and ventricles to the greater cerebral vein (Galen vein). All veins fall into the venous sinuses of the dura mater, from which blood enters the internal jugular vein. Along with this, they have an outflow into the system of the external veins through graduates.
The brain regulates the physiological processes occurring in the body, controls the behavioral reactions of the person and carries out his mental activity. The regulation of all vegetative processes is carried out by maintaining the constancy of the internal environment in the body (blood and osmotic pressure, blood sugar level, pH, body temperature , etc.). The constancy of the internal environment of the organism is maintained according to the principle of self-regulation, which consists in the fact that the deviation of one or another internal constant from the normal level causes excitation in the brain of certain formations that equalize these deviations. This process is carried out by various parts of the brain. In the medulla are such important centers as vasomotor, respiratory. There are also centers that carry out the simplest reactions: sucking , swallowing , chewing , vomiting, sneezing , coughing, blinking, etc. In the hypothalamus, for example, are the centers of hunger and saturation, thermoregulation , sleep and wakefulness. In the structures of the limbic system are the centers of regulation of sexual functions of the body. Higher regulation of vegetative processes is carried out by the cerebral cortex, which very subtly adapts their course to various types of activity of the organism.
Human activity in the external environment is always manifested in physical activity, which is carried out by reducing various muscle groups. The brain finely regulates these processes, ensuring the adaptation of a person to any environmental conditions. The excitations caused by irritation from the outside enter the brain, are distributed over its various subcortical structures, from where they come to the cortex of the big hemispheres. To the cortex, they are sent in two ways. The first is a projection path that continues through the nucleus of the thalamus to the projection areas of the cerebral cortex (visual, auditory, somatosensory). Damage to these areas leads to a violation of the corresponding function (vision, hearing , etc.), which indicates the localization of functions in the cerebral cortex (see Analyzers).
The second way the excitation enters the cerebral cortex passes through the reticular formation of the midbrain. It sends upward excitation to all areas of the cerebral cortex, activating its cells and ensuring the waking state of the brain as a whole. The decrease in stimuli entering the brain reduces the activating effect of the reticular formation on the cortex, which leads to the development of natural sleep. Based on the analysis and synthesis of a large number of stimuli, a response motor reaction is formed in the cortex of the cerebral hemispheres, carried out by the motor area. The constant circulation of excitement between the cortex, the thalamus and other subcortical structures unites the brain into a single whole in the implementation of human behavioral responses. They are built on the basis of unconditioned reflexes (see) and conditioned reflexes (see) and are always accompanied by emotional reactions (see Emotions ).
The human brain carries out mental activity, which consists in the subjective reflection of the objective world and in the formation in connection with this behavior. The leading role in the implementation of mental activity belongs to the cerebral cortex. Possessing great opportunities in the formation of numerous new temporary connections, it allows us to develop and maintain the most complex programs of behavior. Mental activity was especially enriched due to the development of human speech, which led to the emergence of his abstract thinking and allowed him to occupy a dominant position in the animal world. Speech creates the basis for complex forms of meaningful perception of the world and forms the highest mental functions of a person (see Higher Nervous Activity ).