Human Anatomy and Physiology - N. I. Fedyukovich 2003

Nervous System
Physiology of Sleep

It is well known that the alternation of day and night drives diurnal, or circadian, behavioral rhythms. Periodic changes in illumination and associated external stimuli play a particularly crucial role in establishing internal rhythms. The Sleep-wake cycle is one of the manifestations of The Human Body's internal circadian rhythm and is an indispensable prerequisite for life. Human nocturnal sleep is divided into periods of slow-wave sleep, characterized by slow, high-amplitude EEG waves, and rapid eye movement (REM) sleep, during which high-frequency, low-amplitude EEG activity is recorded. The latter is characteristic of an awake individual. Consequently, REM sleep is often referred to as paradoxical sleep, while slow-wave sleep is termed orthodox sleep. An individual who is not yet asleep but in a state of drowsiness typically exhibits an alpha rhythm, the amplitude of which gradually decreases and may completely disappear (Stage A). With the onset of light drowsiness (Stage B), unstable high-amplitude activity emerges. Stage C is usually associated with light sleep, marked by the appearance of low-amplitude slow waves. Transitioning to Stages D and E indicates deep sleep, which is accompanied by an increase in high-amplitude slow-wave activity (delta rhythm). Paradoxical sleep is characterized by low-amplitude, irregular activity with occasional, transient bursts of alpha rhythm and the presence of sharp sawtooth waves. Adults experience 4—6 cycles of REM sleep throughout the night, each lasting approximately 20 minutes. Structure/19.html">The Importance of REM sleep for maintaining well-being increases with age.

Sleep duration is highly individual. In older adults, overall sleep duration decreases, awakenings become more frequent, and periods of deep slow-wave sleep are shortened. Slow-wave sleep is accompanied by a reduction in autonomic tone: pupils constrict, the Skin flushes, sweating increases, lacrimation and salivation decrease, and The activity of the cardiovascular, respiratory, digestive, and excretory systems declines. Slow-wave sleep is also characterized by slow Eye Movements, whereas paradoxical sleep features rapid eye movements. It has been established that the neurochemicals serotonin and noradrenaline are involved in sleep regulation. Slow-wave sleep is regulated by the serotonergic System of the medullary nuclei; a direct correlation has been found between sleep and the overall level of serotonin, its METABOLISM, and the functional activity of these Brain structures. Catecholaminergic Neurons of the Pons and the Midbrain reticular formation act as an antagonistic system responsible for REM sleep and wakefulness. One of the primary neurochemical Functions of slow-wave sleep involves processes related to Protein and RNA metabolism, occurring predominantly in the glial Cells of specific brain structures. Active changes in neuronal membranes during paradoxical sleep are among the reasons for the specific EEG features observed in this functional state.

Sleep disorders lead to The Development of functional impairments of The Nervous system and the onset of diseases.