What Happens When We Sleep?
We all know what it feels like to have a good night’s sleep. We wake up refreshed, rested, and ready to take on the day. On the flip side, when we toss and turn and don’t sleep well, we are irritable, may be forgetful, and generally don’t feel productive the next day. We have an understanding of how sleep makes us feel, but most people haven’t thought about the actual function of sleep from a physiological perspective. Sleep has gained acceptance as a pillar of good health, on equal footing with a balanced diet and exercise. Because of its elevated status in our overall health, there is more focus on understanding what transpires when we sleep and just how vital sleep is to our mental and physical well-being.
Before the 1950s, the accepted belief was that our bodies and minds were dormant during sleep. However, the growing sleep medicine field has produced extensive research which confirms quite the opposite – that many active biological processes happen when we sleep. And since we spend around 1/3 of our life asleep, according to Johns Hopkins Medicine, it is beneficial to understand the multifaceted processes that are occurring. Contrary to popular belief, sleep is not one long event but rather a series of cycles that repeat 4-6 times per night, according to the Sleep Foundation. Each sleep cycle varies in length but, on average, lasts 90-110 minutes. Stages 1 through 3 are referred to as Non-REM (Rapid Eye Movement) sleep or quiet sleep, while stage 4 is known as REM (Rapid Eye Movement) or active sleep.
The first stage of sleep, known as N1, is a transitional state between wakefulness and sleep. During this brief (1-5 minute) stage, brain activity begins to slow, and the muscles relax. During N2, or the second sleep stage, body temperature drops, and heart rate and breathing slow down. This stage is also relatively brief, lasting anywhere from 10 minutes to one hour. The third stage of sleep, known as N3, is also known as deep sleep or slow wave sleep. During this most restorative stage of sleep, brain wave patterns known as Delta Waves help to process the day’s memories and experiences and retain what was learned. Known as Brain Plasticity, this “rewiring” of the brain that occurs during deep sleep also rids the brain of waste. Deep sleep allows us to wake up well-rested and refreshed, but deep sleep diminishes as we age and an extended N2 stage takes its place. During N3, other systems in the body are enhanced. The pituitary gland releases growth hormone during N3, strengthening our immune system, which is critical to fighting infection. Additionally, according to the Cleveland Clinic, the body increases protein production during the N3 sleep stage, which allows for much-needed cell growth and repair.
The well-known REM sleep stage is unlike the prior sleep stages because, during REM, the brain is almost as active as when you are awake. Characterized by its namesake rapid eye movement, the REM stage of sleep returns heart rate and blood pressure close to “awake” levels, with rapid, regular breathing. REM is most associated with the stage where our most vivid dreams occur. And it is interesting to note that while the eyes, heart, and diaphragm can move during REM, our other muscles are temporarily paralyzed via signals from the brain. Research demonstrates that this state, known as muscle atonia, functions to protect us from acting out our dreams. Even our dreams serve a purpose during the REM sleep cycle. Research from the National Institute of Neurological Disorders and Stroke reveals that our dreams act as a type of “mental housekeeping” where partial or unnecessary information is released. It isn’t surprising that the REM stage contributes to creativity and our most critical thinking.
Scientific research has made great strides in discovering what happens in our bodies and minds when we sleep. Sleep is an important time for cleansing, restoration, and regulating various biological processes. Understanding the role of sleep in our mental and physical well-being helps put us on the path to overall good health.
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