Sleep is directly related to human biological rhythms. What do they represent?
It has been established that in the physical world, where all living organisms exist, including man, periodic processes occur due to the movements of the Earth and the Moon relative to the Sun and the movement of the planets. Over several billion years, living creatures had to adapt to daily, multi-day, and annual fluctuations in light, temperature, and other parameters of the world around them.
It is the predictability of these factors that made it possible for all living things to program the features of their behavior, and to prevent the consequences of harmful changes. This allowed to adapt to them and survive.
The human body covers a very wide range of periodic processes from fractions of a second to mega-rhythms with a period of 10 years or more. An example of the oscillatory processes of the body can be the rhythms of the electroencephalogram, respiration, heart rhythms and many other biorhythms at the cellular, organ, organismic and population levels. With the help of biological rhythms, the body can measure time. This mechanism is called “biological clock”, and is closely associated with sleep and wakefulness. A person wants to sleep when his biological clock dictates time for sleep. If this watch fails, insomnia appears. What is regulated by the biological clock that counts the time of human life?
Time sensors are light and dark. Under natural conditions, the alternation of day and night (light and dark), the internal organization of a person obeys a 24-hour circadian rhythm. As a result of this rhythm, the activation phase is replaced by a relaxation phase at certain hours of the day and night. For example, at night the speed of psychomotor reactions, attention, mental and physical performance decreases. This is accompanied by a slowed electrical activity of the heart, a decrease in blood pressure numbers, glucose concentrations in the blood, total lipids, protein fractions, etc. At night, the levels of thyroid hormones, corticosteroids, catecholamines, insulin are minimal, and internal body temperature is lowered. By the pre-dawn hours there is an accumulation of substrates for the biosynthesis of the main hormone of the adrenal cortex, cortisol,blood glucose increases: so the body is preparing for dawn. That is why healthy sleep is important. With insomnia, all biorhythms get off and the body is not ready for daytime life, and at night, instead of sleeping, shows its activity.
However, each person has his own time features of a circadian – circadian – mode. Variants of free current rhythm vary from 20 to 28 hours for different people. On average, the circadian rhythm of individuals ranges from 24.6 to 24.8 and even up to 25 hours.
Such features of a biological clock have a direct impact on the sleep-wakefulness of a particular person, sometimes leading to insomnia. It is established that the near-rhythms are controlled by the deep structure of the brain ( suprachiasmaticus ), located in the anterior hypothalamus.
The experiment showed that during the surgical destruction of this nucleus, sleep changes. It becomes intermittent and short-lived, alternating with short periods of wakefulness, continuing both day and night. At the same time, normal night sleep is completely absent.
The sleep-wake cycle is an example of a circadian rhythm with which other circadian rhythms coincide. For example, internal body temperature is closely related to the sleep-wake cycle. It turns out that it is not always equal to 37 ° C, but varies from 37.8 ° C during the day, dropping to 35.5 ° C in the early morning hours before waking up. For example, a person always wants to sleep when his body temperature begins to decrease. In ordinary life, the decrease in the internal temperature occurs during the day, after it reaches its maximum, and also falls in the evening, thus performing a daily oscillatory cycle. That is why in the evening and in the afternoon people want to sleep.
How does the human body know that the day has come or the night has come? How do biological clocks start?
It turns out that the countdown starts from the moment when a person opens his eyes in the morning and rays of light fall on the retina. Light, irritating the optic nerve, causes nerve impulses from the retina to the nucleus of the hypothalamus suprachiasmaticus . An active life awakens, the internal rhythms of the body are synchronized with the day-night cycle (sun-moon, light-dark) and the biological clock “starts”. Begins the countdown of daily time. We open our eyes in the morning, and our internal clock begins to count down the time with the first ray of light, starting the waking cycle. That’s why you need to get up at the same time! When sleep and wakefulness are disturbed, insomnia arises, since the circadian rhythm of the body is desynchronized with the rhythm of the external environment. This is one of the mechanisms of sleep disorders, which is associated with desynchronization and malfunction of the biological clock.
Desynchronized circadian rhythms may, for example, occur when a person moves to a different time zone. In the new conditions, the sleep-wake cycle should have time to change in accordance with the external light-dark signal, while all internal (hormonal, temperature, etc.) cycles still live their old life, working in the old mode. This leads to insomnia. By the way, precisely because our internal biorhythms are about 25 hours, not 24 hours, it is more difficult for them to shorten their time and work ahead of the phase. It is easier for the body to lengthen its time, that is, lag behind in phase. That is why it is easier to travel from east to west. Such a direction of movement lengthens the day, which is more consistent with the internal circadian 25 hours. But it is more difficult to move from west to east, as the day becomes shorter.
We are aware of the consequences of the transfer of hours to summer time, which desynchronize each year the circulating biorhythm of working people (since the rest can sleep as much as they need), reducing it by one hour with a long follow-up adaptation.
Next, we will separately take a closer look at measures to combat insomnia caused by a long-distance flight or occur in people working on the night shift, age and other cases of sleep disturbance.