Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Higher Nervous Activity
Sleep

Throughout human life, a continuous alternation of two states occurs: wakefulness and sleep. Sleep is a periodically occurring special functional state of the Organism, characterized by the suspension of consciousness, relative immobility, a decrease in Muscle tone and electrical

Brain activity, and specific autonomic reactions. During sleep, a person is unreachable for communication, and external stimuli are perceived very weakly (unless they are excessively intense). Sleep provides a full-fledged rest for all Organs and systems of the body. It is believed that, on average, two-thirds of a human life is spent awake, while sleep occupies the remaining third. During wakefulness, a person performs physical labor, learns, and actively rests. In this state, the functional activity of the brain is heightened. Both sleep and wakefulness have their characteristic EEG patterns.

I. P. Pavlov regarded sleep as a protective inhibition of the Central Nervous system. In his view, this inhibition is necessary for the body to prevent exhaustion and fatigue of the central nervous system structures. Sleep is a physiological need of the organism that ensures the restoration of strength and proper rest. Sleep deprivation leads to decreased performance and reduced attention. Total sleep deprivation for 2 to 3 days results in speech disturbances, hallucinations, and other psychiatric disorders. In animal experiments, sleep deprivation lasting 5 to 12 days led to their death. Thus, sleep is a vitally essential state.

The duration of normal sleep for an adult averages 8 hours. In children, its duration is significantly greater. For instance, under the age of 1, an infant sleeps for the greater part of the day, whereas at 4 years of age, the average is 10–12 hours.

Normal sleep is divided into periods of non-REM (orthodox) and REM (paradoxical) sleep. These periods alternate with one another. Various structures within the central nervous system are responsible for this transition.

Slow-wave (non-REM) sleep accounts for about 80% of total sleep time. The duration of each individual period ranges from 60 to 90 minutes. During these periods, Heart rate, breathing frequency, METABOLISM, and body Temperature decrease. In some individuals, slow-wave sleep may be accompanied by snoring. This phenomenon is associated with an overly prominent soft palate and relaxation of the Tongue Muscles, leading to the tongue falling back. The tongue obstructs the Airways, and as air passes through, characteristic sounds are produced that are not very pleasant for others. Electroencephalographic changes during periods of slow-wave sleep are characterized by the presence of low-frequency, high-amplitude waves (see Fig. 16.1).

Periods of slow-wave sleep are replaced by periods of rapid eye movement (REM) sleep. REM sleep is characterized by rapid Eye Movements behind closed eyelids against a Background of muscle relaxation. During the REM stage, breathing becomes more frequent and The Heart rate accelerates. Its duration averages 15–20 minutes, after which slow-wave sleep resumes. The total duration of rapid-wave sleep is about 1.5–2.0 hours. Electroencephalogram changes are characterized by the appearance of fast, low-amplitude waves resembling those seen during wakefulness. This is the paradox of rapid-wave sleep: the person is asleep, yet brain activity corresponds to wakefulness. It is hypothesized that the REM stage involves the Processing and Organization of Information gathered during the day. Information that is not essential for the person is subject to being forgotten. It is precisely during this period that a person experiences vivid and emotional dreams. If awakened during the REM stage, the individual can almost certainly recount what they were dreaming about. Deprivation of REM sleep leads to various psychological changes: memory impairs, and the person becomes irritable.

Dreams have always fascinated humanity. At different times and in various countries, diverse interpretations of dreams emerged as people attempted to use them to predict the future. Auditory, visual, and tactile images arising during dreams seem to originate "from within." There is a hypothesis that during sleep, a person re-experiences what they have previously seen, heard, or felt, but in a very peculiar chronological order. I. M. Sechenov considered dreams to be "unprecedented combinations of past impressions." Some scientists suggest a link between how a person evaluates the events of the day and what they experience in dreams. S. Freud put forward the hypothesis that dreams reflect a person's hidden desires. Freud introduced the reconstruction of chronological events seen in dreams as one of the Methods of psychoanalysis.

Various sleep disorders exist, with insomnia being one of the primary ones, affecting about 10% of people. One of the severe forms of sleep disorders is somnambulism (sleepwalking). This state is characterized by a person getting out of bed, wandering around the bedroom and the house without waking up. Upon waking, they cannot remember this occurrence.

Various sleep disturbances negatively affect the state of the entire organism, as sleep is a physiologically essential process. The lack of normal sleep implies a lack of proper rest, which leads to various disorders in human psychological and occupational activity.

Certain structures of the central nervous system, particularly the reticular formation, are responsible for the alternation of sleep and wakefulness states.