Excitation and inhibition are the main nervous processes. Without them, not a single motor act, not a single mental experience can be realized.
Excitation and inhibition are two sides, two processes of higher nervous activity. Due to their interaction in the cortex there is an analysis and synthesis of external stimuli in accordance with their importance for the body's vital functions; the dynamics of excitation determines the nature of the response of the body to the effects of its external and internal environment.
The so-called dynamic (mobile) "mosaic" of excitation and inhibition foci in the cerebral hemisphere cortex corresponds to the waking state.
Spatial distribution of these foci is constantly changing depending on the current activity and mental state of the patient. When lecturing, the foci of steady excitement are located in those parts of the cortex that are in charge of speech function, carry out an act of thinking; all other parts of the cortex are in a state of more or less deep inhibition. But when they switch to another kind of activity, for example, they start to play the piano, and the cortical "mosaic" changes at once: the former foci in other groups of cortical cells. In the large hemisphere cortex, humans have 14 to 15 billion nerve cells (neurons). The number of possible spatial combinations of excited and retarded foci in the cortex is truly immeasurable. But each such combination reflects certain moments of different mental states.
What happens to this cortical "mosaic" of awakening when we fall asleep? At some point in the cortex there is a particularly stable center of inhibition. Weak, monotonous stimuli - a lullaby song, swaying, ticking clocks, etc. - can contribute to the formation of such a hearth. From it, as from the center, braking begins to "irradiate" the neighboring groups of neurons, then further and further, extinguishes the hotbeds of excitement encountered on the way, finally, captures the entire cortex, all cortical neurons. There comes a deep sleep without dreams, without any manifestations of mental activity. The cerebral cortex - the "organ of the psyche" - is completely resting.
Consequently, sleep occurs as a result of the predominance of the cerebral cortex inhibitory process. Such inhibition, pointed out I.P. Pavlov. It has "protective" meaning for the body, promotes its rest in general and especially the most finely organized of its apparatus - the cerebral cortex.
Thus, it is possible to say that sleepy inhibition spread over the cortex plays a role of a "guardian angel" for the brain and the whole body. But moreover, it sometimes acts as a "miracle healer", producing an accelerated recovery in the brain cells of those necessary for normal departures of the brain and psyche of the most complex chemical compounds, which are wasted during the daytime stressful activity. Insufficient replenishment of these compounds day by day leads to diseases not only of the brain itself, but also of the organs of the body controlled by it.
It is clear why such diseases are cured by artificially prolonged sleep - the so-called sleep therapy introduced into the medical practice of I.P. Pavlov and his followers.
However, it happens that some disturbing or creative thought or stormy feeling prevents us from sleeping. In such cases, in the cerebral cortex are foci of particularly strong and stable excitement, and they prevent the irradiation of inhibition, the onset of sleep.
If a dream does occur, it will be incomplete, partial. The cortex will retain its "excitation checkpoint". like a lonely cliff in a spilled sea of inhibition. Through it, the sleeping brain can keep in touch with others.
For example, a warrior weary of a hard march sleeps deeply, but with the slightest anxiety he is already on his feet and looking for weapons.
A dream dream dream is another kind of incomplete inhibition of the cortex of the large hemispheres. If the sleep is deep, then the cortex is deeply inhibited and the excitation impulses coming into it from the senses, immediately stalled. There will be no dreams.
Closer to the morning, when the cells of the cortex have enough rest, the protective braking weakens, and the impulses penetrating into it begin to pave the way for themselves in a labyrinth of interwoven neurons. Like a roaming light, excitement moves from one group of cells to another and, by breaking them up, revives that whimsical line of images, mostly visual in nature, which we call a dream. Amazing brightness, vitality of the resulting images! In a waking state, no imagination can draw anything like this. It is the brightness of the images of dreaming and played, apparently, an important role in the emergence of superstitious ideas about the afterlife.
To be continued in the next part https://zen.yandex.ru/profile/editor/id/5d9330af8600e100b06bbabe/5d94922bb477bf00ae02e44c/edit