What Is Sleep?
What is sleep? Sounds like a silly question, but in reality, it isn’t. If something isn’t working, we generally need to know exactly what it is before we can fix it. And the same applies to sleep. The tricky part is that there’s a lot that we don’t really know about sleep. While we know its crucial for health and cognitive function, we still don't fully understand why we sleep, the precise mechanisms of sleep, and the full extent of its impact on the brain and body.
Sleep cycles and stages can vary in length throughout the night and are effected by a number of factors—many of which are entirely within our control
We generally take the idea that sleep is how we rest for granted. But it is a bit of an outlier when it comes to bodily function. There isn’t a time of day in which our hair grows. There isn’t a time of day in which our cuts or bruises do or do not heal. The vast majority of what our bodies do, happens all the time. But sleep, is something else. We have to have it or we literally die. But how exactly it happens and its exact details still escape researchers.
We do know, however that sleep is a fundamental physiological process characterized by a reversible state of reduced responsiveness to external stimuli. That is to say, sleep is something our bodies and minds do when things are quiet and relaxed, and its temporary (at some point we wake up). And despite what we might think, it’s not simply a period of inactivity, but rather a complex and active state during which the brain and body perform essential restorative functions.
Sleep involves a shift in consciousness in which our awareness of our environment is significantly diminished in some way. (Although the extent to which that awareness is diminished differs from person to person and can shift as we age—hence some people are light sleepers, while others are “dead to the world” while they sleep.) Sleep also consists of cycles and stages—although these stages and cycles are not uniform or regular.
A typical sleep cycle can encompass 4 stages of sleep. Although, some sleep cycles will include only stages 2-4.
The most well known of these stages is REM (rapid eye movement)sleep, but there are others, and each is fundamental to the process of healthy sleep. Typically, most people will go through 4-6 sleep cycles each night (per 6-8 hour window of sleep). When you first fall asleep, the first sleep-cycle is usually the most brief, with subsequent cycles lasting longer.
Stage 1 sleep is generally quite short (just a few minutes). Its most associated with falling asleep, and it may or may not appear again throughout the night.
Stage 2 sleep is a part of sleep in which body temperature drops, brain activity slows, eye movement stops, and muscles relax. All together, we spend the majority of our sleep in this stage (sometimes referred to as N2).
Stage 3 sleep is also called ‘deep sleep.’ Its harder to wake up from this stage of sleep, and in this stage, the slowing/relaxing that the body enjoyed in Stage 2 is further and deepened. During Stage 3/deep sleep, the brain exhibits something referred to as delta waves (something you may have heard of, as some sleep remedies include listening to recordings that claim to induce delta waves). This sleep stage is fundamental to restorative sleep. It is believed to aid the immune system and is essential for recovery. Some experts believe that it is also fundamental to creativity and effective memory function. Most of us get the bulk of our Stage 3 sleep in the first half of the night, and it generally lasts for about 20-45 minutes cumulatively. As we age, however, Stage 3 sleep shortens.
The 4th stage of sleep is called REM sleep. While we are in REM sleep, our bodies temporarily restrict our ability to move (although we continue to breath, circulate blood, etc. and our eyes move). In fact, our eyes move sufficiently that they can be seen moving quickly beneath our eyelids—hence the name rapid eye movement (REM) sleep. During this stage of sleep, our brains become more active—almost as if we’re awake. Although dreams can happen at any stage of sleep, we have our most vivid dreams during REM sleep. We get the bulk of our REM sleep in the latter half of the night and it can last for about an hour or so cumulatively. REM sleep is another essential part of sleeping and is believe to be responsible for healthy cognitive function, memory, and brain health.
Sleep is also governed by the planet—which is to say, our internal, biological clock as informed by the cycles of day and night. We are programmed to sleep at night. The ebb and flow of daylight (and also artificial light) directly effects the body’s ability to sleep and wake.
Trouble with sleep can come about for a litany of reasons. Sign up to my mailing list now to learn more and discover how to address your sleep problems.
Lastly, any number of things can effect the length, quality, and frequency of sleep cycles. Age plays a role for all of us. And sometimes chronic health issues such as apnea disrupts and effects sleep cycles as well. Other things that we have more control over, however, also play a part in our sleep cycles. Things like consuming alcohol and caffeine, THC use, travel, emotional and physical health, and sleep hygiene practices factor heavily into our sleep cycles. When sleep cycles go off course, or happen ineffectively, we experience problems with brain function, physical health, and emotional well-being.
All this and more can cause trouble for your sleep. And in subsequent posts, we’ll be digging into sleep problems and what to do about them. If you are not already subscribed to my mailing list to keep up to date with my helpful information, posts, and offerings, sign up now. You definitely don’t want to miss out on this series!
Much gratitude to the National Institutes of Health for their wealth of information and publications which informed this article. Thank you also to the Sleep Foundation and the work of Douglas Kirsch MD, whose article, “Stages and architecture of normal sleep,” also informed this blog post.