11.3 Sleep
Sleep is a natural, restorative state of rest characterized by reduced or altered consciousness and activity and response to one’s external environment. During sleep, sensory activity is relatively inhibited, meaning you are less aware of sounds, sights, and other stimuli, and your interaction with the outside world is significantly reduced. This shift allows the brain and body to focus on internal processes essential for recovery and growth.
Stages of Sleep
Sleep is divided into two main types: NREM (Non-Rapid Eye Movement) and REM (Rapid Eye Movement) sleep. You cycle through these stages multiple times each night, with each full cycle typically lasting around 90 minutes.
Stage 1: NREM 1 (Light Sleep)
- Lasts 1-7 minutes
- You’re just drifting off and can be woken up easily
- Transition Phase: Moving from being awake to being asleep
- What You Might Feel: Sometimes, you can experience brief muscle twitches or the sensation of “falling.”
Stage 2: NREM 2 (Moderate Sleep)
- Lasts 10-25 minutes
- Deeper Than Stage 1: Your heart rate slows down, and your body temperature begins to drop.
- Brain Activity Slows: This is where your brain begins to relax more, preparing for deeper sleep.
- Important For: Resting, but still relatively easy to wake up compared to deeper stages
Stage 3: NREM 3 (Deep Sleep)
- Lasts 20-40 minutes
- Also called “slow-wave” or “delta” sleep
- Hardest to Wake From: If someone wakes you up here, you’ll probably feel groggy and disoriented
- Body Repairs Itself: This stage is critical for physical growth, repair, and overall restoration
Stage 4: REM (Rapid Eye Movement)
- Lasts 10-20 minutes during early sleep and 30-60 minutes later in sleep
- Your eyes move quickly under your eyelids
- Dreaming: Most vivid dreams happen during REM
- Brain Is Active, Body Is Still: Your brain waves look similar to when you’re awake, but your muscles are largely “paralyzed,” so you don’t act out your dreams.
- Memory and Learning: REM helps your brain process information from the day and store it in long-term memory
The illustration below shows how an individual moves through the various stages of sleep over an 8-hour period. Deeper NREM sleep occurs early on in the night, while the duration of REM sleep increases as the night progresses.
Image Description
This hypnogram illustrates a typical sleep cycle pattern, showing alternating REM and non-REM sleep, with a greater amount of deep sleep earlier in the night and increasing REM sleep in the later hours. X-axis: Represents hours of sleep (0 to 8 hours).
Y-axis: Represents different sleep stages:
- REM (Rapid Eye Movement)
- N1 (Light Sleep)
- N2 (Moderate Sleep)
- N3 (Deep Sleep)
Colour Coding:
- Blue (Dreaming): Corresponds to REM sleep.
- Purple (Deep Sleep): Corresponds to N3 sleep.
Graph Line: The orange line tracks the transitions between different sleep stages over time.
Sleep Cycle Observations:
- The person enters deep sleep (N3) within the first hour.
- The deepest sleep occurs within the first 2 hours, after which the person cycles between lighter sleep stages (N1, N2) and REM sleep.
- REM sleep occurs multiple times throughout the night, with longer durations later in the sleep period.
- Sleep becomes lighter as the person approaches wakefulness after around 6 hours.
The Role of Sleep
Sleep is much more than downtime when you are not awake. It is an active and critical part of maintaining physical well-being. Consider the following:
Clean-Up
One of the most important functions of sleep is its role in clearing out waste from your central nervous system, which includes your brain and spinal cord. During deep sleep, your brain activates what’s known as the glymphatic system, which flushes out toxins and metabolic byproducts that accumulate while you are awake. This process only happens during sleep.
If your brain does not activate its glymphatic system during deep sleep to clear out toxins and metabolic byproducts, you may experience:
Toxin Buildup: Accumulated waste products can interfere with normal brain function.- Cognitive Decline: Over time, insufficient clearance of toxins has been linked to issues with memory, concentration, and overall cognitive performance.
- Increased Neurological Risks: Persistent buildup may contribute to a higher likelihood of neurodegenerative conditions like Alzheimer’s disease.
Repair & Regeneration
Beyond the brain, your entire body takes advantage of sleep for repair and regeneration. Muscle growth and repair reach their peak during the deeper stages of sleep, making adequate rest crucial for athletes and anyone engaged in regular physical activity. Your immune system also ramps up during this time, producing and releasing essential cells and proteins that help combat illness and inflammation.
If your body cannot adequately repair and regenerate during sleep, you may face:
- Prolonged Muscle Soreness: Without sufficient recovery, muscles do not fully heal, which can reduce strength and increase the risk of injury.
- Weakened Immune Response: Inadequate sleep can hamper the body’s production of disease-fighting cells, making you more susceptible to infections.
- Slower Healing: Minor injuries or illnesses may take longer to recover from due to decreased repair processes.
Memory Consolidation
As you progress through different stages of sleep, your brain actively organizes and stores information from the day, making it easier to recall later. This is why a solid night’s rest can significantly improve your ability to retain what you have learned or practiced—whether it’s schoolwork, job training, or new skills.
If the brain does not progress through the stages of sleep that organize and store daily information, you may experience:
- Poor Retention of Learned Material: New skills or information may not “stick,” reducing the effectiveness of studying or training.
- Difficulty Concentrating: Lack of consolidated memory can make it harder to focus on complex tasks.
- Overall Cognitive Impairment: Fragmented or insufficient sleep can contribute to confusion, forgetfulness, and slower decision-making.
Sleep Hygiene
Sleep hygiene refers to good habits and practices that help you get consistent and sufficient high-quality sleep.
Activity
Click on the check marks to learn more about good sleep habits to consider.
Text Description
- Keep a Consistent Schedule: Go to bed and wake up around the same time each day, even on weekends. Aim for the same bedtime and wake time daily to stabilize your circadian rhythm, which is your body’s internal clock that helps regulate sleep and wake cycles. Many studies have shown that maintaining consistent bedtimes can improve overall sleep quality and reduce daytime fatigue.
- Limit Screen Time Before Bed: Avoid using phones, tablets, computers, or television at least one hour leading up to bedtime. Blue light emitted from screens can disrupt your body’s production of melatonin, a hormone that regulates sleep, which tricks your body into staying awake for longer. One experiment found that reading on a light-emitting eReader before bed delayed the body’s circadian clock, reducing melatonin levels and overall sleep quality.
- Create a Relaxing Bedtime Routine: Wind down with calming activities like reading or gentle stretching. Avoid vigorous workouts right before bed.
- Optimize Your Sleep Environment: Keeping your bedroom cool, dark, and quiet and investing in a comfortable mattress and pillows. Environmental factors like ambient light, noise, and temperature have been consistently linked to sleep disruption in clinical studies.
- Watch Your Diet: Avoid large or heavily caffeinated meals close to bedtime, as both caffeine and high-calorie foods can interfere with sleep. Studies have shown that caffeine consumption, even six hours before bedtime, can significantly reduce total sleep time and sleep quality.
Did you Know?
According to the National Sleep Foundation:
- Adults need 7 to 9 hours per night
- Teenagers need 8 to 10 hours per night
- Children need 9 to 12 hours per night
