The Definition of Sleep and How it Affects Your Body
The pace of modern life often makes getting enough sleep a challenge. But a good night’s rest is vital to your health and well-being, and a regular pattern of quality sleep helps your body to perform its many restorative functions.
Getting an adequate amount of restful sleep on a regular basis is important for your mental and physical health, especially during times of high stress. This is because during sleep your brain clears out the proteins and other waste that accumulate during stressful situations, helping to restore normal brain function and boost the immune system.
Your body cycles through four or five stages of non-REM (NREM) and REM sleep each night. Each cycle takes about 90 to 120 minutes to complete and includes three or more periods of stage two NREM sleep, followed by a period of dreaming during REM sleep, and then back again to NREM sleep. During NREM and REM sleep, your eyes move rapidly behind closed lids, you are briefly paralyzed, and your breathing and heart rate accelerate. During this phase of the sleep cycle, you may also experience vivid dreams that can sometimes be difficult to remember after you wake up.
Most people understand that sleeping is necessary for survival, but few know what actually happens in your body when you are asleep. Sleep affects virtually every tissue and system of the human body, including the brain, heart, lungs, immune system, metabolism, mood and ability to fight disease. It is believed that a lack of sleep or getting poor quality sleep can increase the risk of many diseases, including cancer, heart disease and diabetes.
What is it about sleep that makes it so important to our bodies and minds? Scientists are working hard to answer this question and are learning more and more about how it works. There are three main definitions of sleep: physiology, behavior and phenomenology.
The physiology of sleep is defined by changes in the electroencephalogram, or EEG, that occur during sleep. While sleep is a universal phenomenon, these EEG changes can vary slightly between individuals and can be affected by factors such as age, diet, medications and even the environment.
In the behavioral and phenomenological definitions of sleep, scientists use subjective reports about sleep to distinguish it from wakefulness or other states. Historically, this has been done using questionnaires, but more recently, scientists have used noninvasive, in-vivo brain imaging to characterize sleep. These techniques can reveal the onset of different stages of NREM and REM sleep, and indicate when an individual is experiencing a dream or is unconscious.
The neurobiological study of sleep has shown that sleep is a complex and dynamic process that influences nearly every cell in the brain and body. While the exact mechanism of this phenomenon is still unclear, there are indications that sleep is orchestrated by the activity of large cortical networks and, at the same time, regulated by local modulations in subcortical structures (Krueger et al., 2023). Human intracranial recordings have emphasized that there are dissociations between different brain regions during sleep, particularly between the neocortex and hippocampus (Duran et al., 2018).