Dive into the intricate science of sleep and discover the biological secrets behind your nightly slumber in this second part of our two-part blog on the importance of sleep.
Read part one here: The Astonishing Impact of Sleep on your Health
Sleep is a fundamental state that all animals, including humans, experience daily. Sleep scientists have categorized this unconscious state into two main categories: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep, based on the rapid movement of the eyeballs. While the exact reason for these eye movements remains speculative, two primary theories exist. One suggests that the eyes move because we are actively observing things in our dreams, while the other proposes that prolonged stationary eye positions could harm them by impeding the drainage of essential fluids, similar to what occurs in glaucoma.
REM sleep should typically constitute about 25% of your total nightly sleep time, while non-REM sleep makes up the remaining 75%. Non-REM sleep, in contrast to REM, can be further subdivided into three or five categories. The simplified three-category model divides non-REM sleep into N1 (the initial stage of falling asleep), N2 (light/core sleep), and N3 (deep sleep). Each stage of non-REM sleep is essential and exerts distinct effects on the body and brain.
Wondering what triggers the urge to sleep? Two independent biological processes contribute to the phenomenon of feeling “sleepy.” The first is your circadian rhythm, a cellular response to the presence or absence of light, regulated by a part of the brain known as the suprachiasmatic nucleus. This “body clock” precisely tracks the 24-hour day, with recent research indicating its ability to estimate time within a 13-minute window. This explains why some individuals can consistently wake up at the same time every day, thanks to an active suprachiasmatic nucleus.
The second biological process involves the buildup of the neurotransmitter adenosine in the brain. Adenosine gradually accumulates from the moment you wake up until you fall asleep, binding to specific receptors in the brain. The more receptors adenosine occupies, the more profound your feeling of tiredness becomes. Caffeine, with a similar three-dimensional shape to adenosine, can fit into these receptors, temporarily blocking adenosine and reducing fatigue. However, caffeine’s effect lasts only 6-12 hours, as it metabolizes out of the brain, allowing adenosine to regain its influence. During deep sleep (N3), adenosine is efficiently flushed out of the brain. Inadequate sleep can leave some adenosine unflushed, resulting in grogginess upon waking.
Curious about what transpires during the sleep cycle? The journey typically begins with the non-rapid eye movement (non-REM) N1 phase, or the initial act of falling asleep, which lasts for about 5-7 minutes. This stage is often described as being “half-asleep,” during which you are easily awakened. Next comes the non-REM N2 phase, known as light or core sleep, constituting approximately 45% of your total sleep time. In this phase, your breathing rate, muscle tone, and body temperature decrease, and teeth grinding may occur. Sleep spindles become active during this phase, believed to play a crucial role in memory consolidation.
The subsequent stage is non-REM N3 or deep sleep, accounting for 25% of your total sleep time. In this phase, your body repairs injuries, rebuilds muscles, and rejuvenates the immune system, including its capacity to combat cancer. Additionally, this stage is associated with sleepwalking, night terrors, and bedwetting. Up to 70% of your deep sleep occurs in the first half of the night.
The final stage of the sleep cycle is Rapid Eye Movement (REM) sleep, also known as paradoxical sleep because brain activity in this phase closely resembles wakefulness. REM sleep should make up about 25% of your total sleep each night. Interestingly, REM sleep is not restful; in fact, brain metabolism can be 20% higher compared to when you’re awake. During REM, you experience vivid dreams and nightmares, and both men and women may have genital erections. Research suggests that REM sleep plays a significant role in cognitive function, emotional regulation, and potentially offers protection against dementia in later life. Up to 70% of your REM sleep occurs in the second half of the night.
We all know sleep is vital to our general wellbeing, but understanding the why and how our bodies need sleep, and that fostering good sleeping habits and patterns, can lead to significant and impactful changes in our health and human functioning.
We hope you enjoyed our special two-part blog series on sleep–sweet dreams, #yyc!