The degree of sleep quality dictates the degree of quality of life, since it conditions physical and mental health, with direct expression in the level of vitality. Sleeping too little or having ‘bad’ nights affects the so-called ‘quality of life’. sleep healthSleep is a natural physiological process that is indispensable for good intellectual health and, consequently, for productivity, the good performance of the immune system, the maintenance of all rebalancing processes and the regeneration of our cells.
Knowing the mechanisms of sleepby analysing information such as the circadian cycle and sleep pressure, we can take steps to improve the quality of our sleep. All of our body’s functions are cyclical. So sleep is also made up of sleep cycles and each cycle is made up of phases. There are two main phases of sleep: the deep phase, known as the non-REM phase, and the REM phase, a more superficial phase.
What is Sleep?
Sleep is a natural physiological state and indispensable to life, it is a fundamental component of life and therefore of physical and mental health, without it we would die.
The biological processes of sleep are regulated by sleep pressure and the circadian cycle. These are the phenomena that lead us to feel sleepy, fall asleep, stay asleep and, in the end, wake up. Neurotransmitters are the chemical mediators that act as commands to signal and activate the rhythms and phases of sleep and wakefulness.
The functions of sleep are numerous and all of them contribute to our homeostasis, i.e. the processes that guarantee internal balance. It is during sleep that cells, tissues and organic functions are rebalanced, repaired and regenerated. Therefore, getting enough sleep at the right time will strengthen the immune system, hormone regulation, cardiovascular balance, brain regeneration with cognitive repercussions (memory, concentration, decision-making, creativity, etc.) and the emotional response to daily challenges (greater serenity, tolerance, resilience, humour).
It’s worth noting that during the growing years, growth hormone is secreted during sleep, particularly in the early hours of the evening. Therefore, children who sleep little and go to bed late will have their growth and robust physical and mental health jeopardised.
The Mechanisms of Sleep
All of nature, all of life on this planet is governed by cycles that create rhythms. It is the guarantee of rhythms that allows life to be balanced and ecosystems to be conserved. We are nature and we are made up of a giant ecosystem of cells and these have rhythms and preserving them is vital.
Our daily rhythm alternates between wakefulness and sleep. We are governed by the circadian cycle or rhythm, which is nothing more than an internal clock in which each organ and system has its own working and resting hours.
The circadian rhythm, which indicates ‘when’ to sleep, is governed by solar time, and there is a synchronisation between the brightness of the day (light-dark) and our body’s internal time. In the case of sleep, over the course of the night, the production of specific neurotransmitters is induced which orchestrate the entire process from the onset of sleep to its maintenance and awakening.
The tiny pineal gland at the base of the brain is endowed with photosensitive cells, identical to those in the retina and capable of translating the light signals that enter through our eyes into chemical signals, which in this case are two neurotransmitters – melatonin, which induces sleep in response to darkness, and serotonin, which induces awakening in response to dawn. GABA, another neurotransmitter, promotes relaxation and preparation for sleep by reducing brain activity.
Sleep Phases
Sleep stages are distinct physiological stages that the body goes through during sleep. The two main stages are REM (Rapid Eye Movement) sleep and Non-REM (NREM) sleep, which together form a sleep cycle made up of these two phases.
Non-REM sleep is the stage with the longest duration and is made up of three phases:
- Phase 1 is the initial phase that lasts just a few minutes and corresponds to the transition phase between wakefulness and sleep, during which the body and mind begin to relax, the heart rate slows down and the muscles relax (which can lead to involuntary movements to release muscle tension).
- Stage 2 is light sleep and represents the majority of sleep time. In this phase the entire body’s metabolism is reduced: a reduction in brain activity, heart rate and body temperature.
- Stage 3 is deep sleep. This is the most restorative and regenerative stage on a physical level.
REM sleep is the final phase of each cycle. It is characterised by rapid, involuntary eye movements and intense brain activity. It corresponds to the dream phase. This is the phase that is essential for memory consolidation (converting short-term memory into long-term memory).
Sleep Cycles: How Do They Work?
Each sleep cycle lasts between 90 and 120 minutes and, during a night’s sleep, we will have between 4 and 6 sleep cycles. A sleep duration varies with age and stage of life – the younger you are, the more hours of sleep you need. Newborn babies sleep up to 17 hours; at pre-school age, up to 13 hours; at puberty, up to 11 hours; in adulthood, we sleep between 6 and 8 hours; at older ages, sleep tends to be shorter.
Each sleep cycle is made up of alternating sequences of non-REM and REM sleep phases, which vary in length according to life stage, season and geographical latitude.
Sleep patterns refer to the ways in which sleep is distributed over a 24-hour period, which includes the times of day, its duration and the organisation of sleep cycles and phases. They also vary from person to person, depending on age and lifestyle, and are therefore influenced by biological, behavioural and environmental factors. Understanding the organisation of nocturnal cycles and their changes throughout life helps to adopt habits that promote more restful sleep, adjusting to the needs of each phase.
Disorders Related to Sleep Mechanisms and Cycles
Sleep disorders are increasingly common in the Western world and affect millions of people. They correspond to dysregulations in sleep cycles or sleep mechanisms and therefore jeopardise sleep health, well-being and quality of life. The most common are insomnia, sleep apnoea and narcolepsy.
Insomnia is the most common disorder. It is characterised by difficulty initiating sleep, maintaining it or resuming it after waking up during the night, reducing sleep health by reducing deep sleep and causing fragmentation of sleep cycles. It is usually conditioned by emotional and psychological factors.
Sleep apnoea is a condition in which breathing is suspended several times during the night, interrupting sleep and altering the dynamics of sleep cycles and phases. Not all of its causes are fully understood, the main ones being blockage of the airways, which is usually associated with obesity.
Narcolepsy is a neurological disorder characterised by extreme sleepiness during wakefulness, with the possibility of sudden, uncontrollable sleep episodes. It is a serious condition because it compromises the normal rhythm of life, and can jeopardise driving safety and the performance of professional duties. All these irregular cycles jeopardise vital biological functions such as immunity, hormonal balance, physical recovery and memory.
Conclusion
Now that they have been the phases of sleep, their mechanisms, and how a healthy cycle is characterised, it’s clearer to see why sleep is so important the importance of sleep and the impact it has on your physical, mental and emotional balance. The preservation of all sleep mechanisms, namely sleep homeostasis and the circadian cycle, guarantees the balance of all the body’s systems and functions and greater vitality. The balance between deep and shallow sleep phases is crucial for memory consolidation, brain revitalisation and physical recovery.
You will then have been able to recognise that it is in your hands to improve the quality of your sleep by analysing yourself and identifying what corrections you need to make to your habits and routines in order to improve your sleep and, therefore, the quality of your life. And if you’re interested in learning more about this subject, I suggest reading the articles below, as well as waiting for future articles on this site.
A good night’s sleep is priceless!
Biography
- Fernandes, R. M. F. (2006). O sono normal. Medicina (Ribeirão Preto), 39(2), 157-168. DOI:https://doi.org/10.11606/issn.2176-7262.v39i2p157-168
- Amaral, T. P. C., Tessarin, G. W. L., Bonfietti, L. H. F. S., Ferro-Alves, M. L., Binhardi, T. D. R., Pereira, L. V., … & Dekon, S. F. C. (2013). Fisiologia do sono: características de um sono normal. Revista de Odontologia da UNESP, 41(Especial), 0-0.
- de Moraes, V. R., Pereira, J. C., & de Almeida, C. G. (2024). A fisiologia do sono e seu impacto na memória: uma revisão de literatura. Brazilian Journal of Health Review, 7(10), e75331-e75331. DOI: https://doi.org/10.34119/bjhrv7n10-228
