Physiological characteristics of sleep

So what is a dream?

Unfortunately, science is not yet fully capable of answering this question exhaustively. The mechanisms of sleep and wakefulness, like the mechanisms of the brain, are extremely complex. And nevertheless let’s try, at least outwardly, to characterize the state of sleep. Let’s take a closer look at sleeping people and animals. What is most typical for sleep?

When a person or an animal sinks into sleep, they stop responding to normal environmental stimuli. Try asking a question to a sleeping person without raising your voice. A thicket of everything you will not get an answer, and to awaken the sleeping one has to raise his voice.

Its reaction to touch, a flash of light, etc., is insignificant. This is because the susceptibility of our sense organs, sight, hearing, taste, smell, touch, etc., decreases sharply during sleep.

This condition does not occur immediately. Initially, drowsiness develops, during which the eyelids become “heavy”, I want to close my eyes. If you have ever been sleepy while reading, then you probably noticed that you can read the same phrase several times without recognizing its meaning.This means that the organ of vision still performs its function, but in vain: the brain no longer perceives it. However, this is not a dream. The slightest rustle – and the person again reacts to the environment. This is repeated again and again. And finally, a real dream comes when everything around you becomes indifferent. The dream came into its own …

So, the main sign of sleep is turning off from the surrounding reality and as an expression of this is the closing of the eyelids covering the eyes, which is accompanied by turning the eyeballs upwards.

No less characteristic sign of sleep is a decrease in motor activity. The state of sleep is like some kind of temporary stupor, which can catch a person in any position. This is especially evident in young children, who may fall asleep sometimes in the midst of a game, in the most unexpected situations.

And, finally, it is very characteristic for a person to turn off the consciousness in a dream. Even if a sleeper answers a question, it is often wrong, and when he wakes up, a person often denies the fact that he answered you. So he does not remember this. But do you always remember? About this conversation will be yet to come.

Here, perhaps, all the main, most vivid, conspicuous signs of sleep. The question remains: is every dream the same? Is animal sleep different from human sleep? What types of sleep are found in nature? Is it possible to cause sleep arbitrarily, that is, at will? And, on the contrary, is it possible to overcome it? How much should I sleep? ..

Sleeps only the brain or the whole body?

Sensations, consciousness … For everyone now it goes without saying that these phenomena are primarily associated with the activity of the brain. The disappearance of sensations and consciousness during sleep indicates that the brain is “asleep.” But is it just the brain?

To answer this question, scientists conducted observations on the activities of various organs and body systems during sleep. It turned out that during sleep, many organs switch to another mode of operation. D yhanie becomes less, reduced heart rate, blood supplying organs and tissues.Reduced blood pressure in the vessels that deliver it to the working bodies, the muscles relax. Body temperature drops by 0.5-1 °. Obviously, there is some connection between the activities of all systems and organs, which does not allow for the disruption of the general mode of the organism.

Let’s try to figure it out.

Heart rate (heart rate) becomes less common in humans during sleep at 10-15 beats per minute. If a healthy adult’s heart rate varies on average between 60-70 beats per minute, then in a state of sleep, the heart makes about 50-60 beats per minute. With each contraction, the heart throws about 65 to 70 milliliters of blood. This means that in the state of sleep, the heart pushes 30–35 liters of shelter less for an hour in blood vessels than during wakefulness, and for 7–8 hours of sleep at night, 240–250 liters less than for the same period of time during the day.

But after all, the blood carries nutrients and oxygen to the tissues and cells of our body, which are necessary for the maintenance of their vital activity. The absorption of these substances and the allocation of unnecessary waste product, ie, the metabolism in tissues, its intensity are directly dependent on the amount of blood flowing. This means that a decrease in blood delivery to tissues during sleep should be accompanied by a decrease in the intensity of metabolism. Indeed, studies conducted on sleeping people showed that during sleep, the intensity of energy exchange decreases by 8-10% compared with the intensity of exchange in the waking state.

These observations are consistent with the data on the study of respiration. It has been found that breathing becomes less frequent during sleep (although somewhat deeper). Slowdown occurs mainly due to an increase in the duration of expiration. In general, the volume of minute pulmonary ventilation, i.e., the amount of inhaled and exhaled air, is reduced by about two liters, although the process of enriching blood with oxygen, which it delivers to the tissues, takes place in the lungs. Thus, the process of oxygen absorption from the environment during sleep is also significantly reduced.

All this suggests that during it “rest” along with the brain and internal organs, providing the vital activity of cells and tissues. At the same time, a reduced level of metabolism in the body is quite sufficient to maintain its normal existence (obviously, due to the fact that energy expenditure during sleep is much less mainly due to maximum muscle relaxation).

Thus, during sleep, the body leads a more economical lifestyle. But, despite the reduced level of energy metabolism during it, this level is sufficient to prepare the body for a new wakefulness cycle. After awakening, a healthy person again feels awake, full of strength, ready for vigorous activity, both physical and mental.

Electrophysiological characteristics of sleep

Electric “whirlwinds” are constantly sweeping through the brain. They can be registered by simultaneously diverting electrical oscillations from many points of the head. For different physiological states, the resulting electroencephalograms (EEG) will have a peculiar pattern. During the transition from wakefulness to sleep, i.e., in the process of falling asleep, as well as during the awakening period, the EEG changes have a fairly specific and consistent order. Although the information that is embedded in the EEG is still far from being deciphered, nevertheless, shifts in the overall electrical activity are quite typical for different depths of sleep, so much so that even automatic methods for controlling the depth of anesthesia are used in surgery. They are based on timely recording of EEG changes with the help of special devices that monitor its changes. The features of EEG in the states of sleep and wakefulness have been known for a long time. However, relatively recently, interesting data were obtained that made it possible to re-evaluate their significance.

Animal observations have shown that falling asleep is accompanied by the appearance of slow waves in the electroencephalogram, similar to those observed during low-frequency stimulation of thalamic nuclei. However, after about an hour, these slow-wave characteristic waves are large. the amplitudes disappear and are replaced by fast, high-frequency oscillations of small amplitude characteristic of the waking state of the animal. Nevertheless, there are no signs of awakening at this time, and tests with irritations showed that sleep in this period becomes deeper — more powerful stimuli are needed to wake the animal. Such a dream lasts 10–20 minutes, after which slow waves appear again in the animals’ EEG.

It is curious that “fast” sleep (t, e. With fast high-frequency electrical activity) never occurs in animals immediately, but only after the previous period of “slow” sleep (i.e., sleep with slow waves in the EEG). But for 6-8 hours of sleep, sleep attacks usually occur several times, quite regularly, with an interval of approximately one and a half hours.

The American scientists Dement and Kleitman and the Frenchman Juve called sleep with fast activity a “paradoxical” dream, since the EEG of animals during this period of sleep completely resembles the EEG of awake animals. At the same time, it is precisely this stage that corresponds to the most pronounced shifts in the body, characteristic of sleep: complete relaxation of muscles, slowing of heart contractions, lowering of blood pressure, etc. However, in animals during “fast” or “paradoxical” sleep eye movements, twitching of limbs, tail, licking are observed.

During the sleep, an EEG, breathing, an electrocardiogram were recorded during sleep, and with light sensors fixed on the eyelids – eye movements. It turned out that people also have slow rhythms during the night, fast in EEG about 4-5 times (Fig. 3). During these short periods of “fast” sleep, they also observe rapid eye movements, blood pressure changes, and the regular rhythm of heart contractions is disturbed.

It is interesting that if a person is awakened during a “fast” sleep, in most cases the sleeper will say that he has just had a dream. If a person is awakened during a “slow” sleep or 10–15 minutes later after a period of “fast” sleep, he will usually answer that he has not seen any dreams. On this basis, Juve and others suggested that people see dreams during a “fast” sleep. Observed eye movements, fluctuations in heart rate and respiration seem to reflect the experiences experienced in the dream.

Scientists have tried to wake people up at the time of the onset of “fast” sleep, in order to prevent them from seeing dreams. At the same time, despite a sufficient overall duration of sleep, after 5-6 days they had mental disorders. And animals deprived of “fast” sleep for several days, died, although in general they slept.

All this suggests that the “fast” sleep is of particular importance for the functioning of the body.

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