What Happens When You Sleep?

Sleep is a natural part of life that is so important to every aspect of our health.  We need sleep to repair, rejuvenate, create hormones effectively, process memories at much more.
It is an essential part of your daily routine as you spend about one-third of your time doing it. However there are many people that aren't getting enough of it at the right times, is as essential to survival as food and water.  Without sleep you can’t form or maintain the pathways in your brain that let you learn and create new memories, and it’s harder to concentrate and respond quickly.

Sleep Stages

Sleep is divided into two categories: REM and non-REM sleep. You begin the night in non-REM sleep followed by a brief period of REM sleep. The cycle continues throughout the night about every 90 minutes.
Deep sleep occurs in the final stage of non-REM sleep.

Non-REM sleep
Stage 1 of non-REM sleep lasts several minutes as you move from being awake to being asleep.
During stage 1:

• your body functions — like heartbeat, respiration, and eye movements — begin to slow
• your muscles relax with only occasional twitches
• your brain waves start to slow down from their wakeful state
  
  

Stage 2 accounts for about 50 percentTrusted Source of the total sleep cycle. This is the stage of sleep you may fall into more than any other throughout the night.
During stage 2:

• your body’s systems continue to slow and relax
• your core temperature drops
• your eye movements stop
• your brain waves are slow, but you have some short bursts of activity
  
  

Stages 3 and 4 are when you experience deep sleep.
During these stages:

• your heartbeat and breathing become their slowest as your muscles relax
• your brain waves become the slowest they’ll be while you’re asleep
• it’s difficult to awaken even with loud noises

Deep sleep is also referred to as “slow wave sleep” (SWS) or delta sleep.
The first stage of deep sleep lasts anywhere from 45 to 90 minutes. It lasts for longer periods in the first half of the night and becomes shorter with each sleep cycle.

REM sleep or what some call Stage 5, or your first stage of REM sleep,occurs about 90 minutes after moving through non-REM stages.
During this stage:

• your eyes move rapidly from side to side
• you experience dreaming as your brain activity increases to a more wakeful state
• your heart rate increases to near its wakeful state
• your breathing becomes faster and even irregular at times
• your limbs may even become paralyzed

​What are the benefits of deep sleep?
​Glucose metabolism in the brain increases during deep sleep, supporting short-term and long-term memory and overall learning.

Deep sleep is also when the pituitary gland secretes important hormones, like human growth hormone, leading to growth and development of the body.

Other benefits of deep sleep include:

• energy restoration
• cell regeneration
• increasing blood supply to muscles
• promoting growth and repair of tissues and bones
• strengthening the immune system

The Anatomy of Sleep

Every person has an internal timekeeping system known informally as the "circadian clock," which is located in the hypothalamus near the front of the brain. The circadian clock is programmed to reset, or "entrain," every 24 hours. This 24-hour cycle, the circadian rhythm, is guided by natural light and plays a major role in hormone production, as well as mood, appetite and digestion, body temperature, and other bodily functions.

The hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal.  Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.  Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.  

The brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep. The brain stem includes structures called the pons, medulla, and midbrain. Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem.  The brain stem ESPECIALLY the pons and medulla also plays a special role in REM sleep sending signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

This clock consists of roughly 20,000 nuclei clustered together to form a structure called the suprachiasmatic nucleus (SCN). During the day, the retinas in your eyes perceive natural sunlight and transmit signals through a nerve tract that leads directly to the SCN. These signals inform the brain whether it is day or night.
In the evening as natural light begins to disappear, the pineal gland in your brain will produce melatonin, a natural hormone that induces feelings of relaxation and sleepiness.

The thalamus acts as a relay for information from the senses to the cerebral cortex, this is the covering of the brain that interprets and processes information from short- to long-term memory.  During most stages of sleep, the thalamus becomes pritty quiet, letting you tune out the external world.  But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

The pineal gland which is located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down.  People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.  

The basal forebrain, near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system.  Release of adenosine (a chemical by-product of cellular energy consumption) from cells in the basal forebrain and probably other regions supports your sleep drive.  Caffeine counteracts sleepiness by blocking the actions of adenosine.

The amygdala, an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep. 

​When you wake up in the morning and your eyes perceive natural light, the body will produce another hormone, cortisol, that promotes alertness and wakefulness. The brain stem also communicates with the hypothalamus to produce GABA, a hormone that decreases arousals and helps the body wind down.
In addition to circadian rhythm, your sleep is also regulated by a process called sleep-wake homeostasis. Also known as your sleep drive, this mechanism regulates feelings of tiredness and wakefulness. For every hour you're awake, your sleep drive will become stronger, and these feelings will culminate right before you go to bed.

Your circadian rhythm and sleep-wake homeostasis do not exist in a vacuum. Circadian rhythm disorders can cause you to feel tired and alert at times of the day that do not align with natural light cycles. Examples range from mild conditions such as jet lag to more serious conditions such as advanced or delayed sleep-wake phase disorder, irregular sleep-wake rhythm disorder, and shift work disorder. Factors that can affect or alter your sleep-wake homeostasis include light exposure, diet, stress, medical conditions, and your sleep environment.

When sleep goes wrong

In a 2014 Ted Talk program, neuroscience researcher Jeff Illiff presented mind-blowing research on how the brain deals with its “waste.” He explained that researchers were astonished to find that when we sleep, channels open up around the blood vessels in the brain. These channels flush the brain with cerebrospinal fluid (CSF), which effectively cleans the brain, taking away the waste products from normal metabolism.
​
When you’re not getting enough sleep, or if your quality of sleep is poor, all of the positive things that happen in sleep—as described above—decrease. Your body is unable to repair effectively, biological processes are disturbed, and there are significant effects on brain function and cognition.

Lack of quality sleep can impact:

• Heart health. Your blood pressure decreases while you sleep, which makes it easier for your cardiovascular system to function. So While you sleep your heart takes a rest. It doesn’t need to pump large amounts of blood to your muscles or digestive system. Of course it continues to pump blood to your brain and all around the body, just less vigorously. Lack of sleep puts an increased strain on your heart.
• Hormonal systems. Your hormonal or endocrine system produces chemicals essential to every cell, system and organ in your body. Lack of sleep interferes with hormone release and cellular repair, growth, blood pressure, blood sugar, and sexual health. In teenagers, lack of sleep can interfere with puberty.
• Weight maintenance: Your body produces hormones in response to appetite and digestion. These include ghrelin, which makes you feel hungry, and leptin, which tells you you're full. Lack of sleep can elevate your ghrelin levels while decreasing your leptin levels. As a result, you may eat more during the day than you otherwise might after a good night's sleep.
• Insulin production: Insulin is a hormone that regulates how much glucose, or sugar, is in your blood. Your glucose levels increase following meals, so your body produces more insulin. When you sleep, your glucose and insulin levels decrease.
• Memory. Lack of sleep limits consolidation of memory, making it difficult to lay down long-term memories.
• Cognitive performance. Lack of sleep will reduce focus, slow processing, and cause errors and may also contribute to poor decision-making and impulsivity.
• Motor skills. Lack of sleep can make you more likely to make mistakes and have an accident.
• Mood. Lack of sleep increases the risk of negativity, depression, anxiety and may worsen serious psychiatric conditions such as bipolar disorder.
• Immune health. Lack of sleep weakens the immune system making you more prone to infection. The immune system is essentially your body's defense shield against diseases and infections. While the immune system doesn't shut down during sleep, certain aspects are more active than others.
• Energy conservation: Many experts believe sleep is vital to health because it helps us conserve energy. Your metabolism operates at lower levels while you're asleep, which decreases the amount of energy you need. One study estimates eight hours of sleep can conserve up to 35% of the energy you require to function during the day.​

What Happens to Your Body When You Don't Sleep?

Sleep deprivation often leads to tiredness during the day. You may wake up feeling less refreshed and alert than you might after seven to nine hours of uninterrupted sleep, and this can affect how you perform in different professional and social settings. Other immediate side effects of inadequate sleep include anger and irritability, impulsivity and poor decision-making, and trouble concentrating.
HOWEVER chronic lack of sleep can lead too...
It can be very detrimental to your long-term health.
Complications that may arise include:

• Obesity: Inadequate sleep interferes with production of your ghrelin and leptin hormones that regulate feelings of hunger and satiation, respectively. This may cause you to eat more during the day, which can lead to unhealthy weight gain and obesity.
• Heart disease and stroke: Sleep allows your blood pressure levels to temporarily  decrease during certain stages of the sleep cycle. Since blood pressure drops during sleep, less sleep means a smaller percentage of your 24-hour circadian cycle is spent in this low blood pressure zone. High blood pressure can be a risk factor for heart disease and stroke.
  
• Type 2 diabetes: Sleep plays a role in insulin production and glucose levels. Not getting enough rest can elevate your blood sugar to unhealthy levels and put you at higher risk of Type 2 diabetes. Additionally, obesity is considered a major risk factor for this disease.
• Poor immunohealth: Without enough time to restore itself, your immune system's defense barriers can weaken due to inadequate sleep. This makes it harder for your body to stave off diseases and infections, putting you at a higher risk of getting sick.
• Stunted growth and development: The hormones that regulate growth and development, build muscle mass, and repair cells in children and adolescents are triggered during deep sleep. Those who don't receive enough sleep may not grow and develop properly.
• Accidents and injuries: Lack of sleep decreases your ability to concentrate and reduces your reaction time. This puts you at higher risk of hurting yourself, especially at work or while driving. Roughly 100,000 car accidents – and 1,500 deaths – occur each year due in part to driver sleepiness.
• Impaired performance: People who don't get enough sleep are less likely to succeed in school and tend to commit more errors at work. Even minor sleep debt can contribute to these impairments and negatively affect your overall wellbeing and cognitive performance.

Sleep Hygeine

Sleep hygiene is a collection of practices or behaviours around sleep that help to promote melatonin production. Improving our sleep hygiene helps prepare our body for good quality, restorative sleep.
These include:

• Set a sleep schedule and stick to it. Try to go to bed at night and awaken in the morning around the same times, even on weekends. This helps to regulate the body’s sleep cycles and circadian rhythms.
• Exercise Regular exercise of adequate intensity can promote muscle relaxation and deeper sleep later on.
• Caffeine, try to avoid drinking caffeinated beverages 4-6 hours before bedtime.
• Electronic devices, avoid an hour before bed, especially those emitting blue light such as smartphones, tablets, and televisions.
• Temperature, ensure a comfortable temperature as feeling too hot or cold can disrupt sleep.
• Create calming bedtime rituals such as practicing deep breathing exercises, doing light yoga stretches, or listening to soothing relaxing music. Many meditation podcasts, apps, and YouTube videos offer these tools for free.
• Sunlight, spend time outside in the sun during the day. Exposing your body to natural light during the day can help maintain a healthy circadian rhythm.
• Limit your nap time to no more than 30 minutes.
• Limit your screen time an hour before sleeping. TVs, phones, and other electronic devices emit blue light, which can interrupt the hormones that help you fall asleep.
• Foods. Swap out sugary and starchy foods, for vegetables and fruits. A high glycemic index diet, which is associated with foods with high amount of simple carbohydrates such as potatoes, white rice and white bread, can quickly increase blood sugar. Although high glycemic meals were shown to help healthy volunteers fall asleep in experimental conditions higher intakes of dietary added sugars, starch, and nonwhole/refined grains have been associated with a higher risk of developing insomnia over time. By contrast, higher nonjuice fruit and vegetable intakes were significantly associated with lower chances of developing insomnia.

​What if I am a Shift Worker?

People who work overnight shifts, early morning shifts, or rotating shifts (both day shifts and night shifts) may develop something called shift work disorder (SWD). Studies show that those with SWD have poorer sleep quality than day workers. They may take longer to fall asleep, experience insomnia, and feel excessive sleepiness while awake. This is caused by attempts to sleep in daylight, which opposes natural circadian rhythms. Poor sleep hygiene further aggravates the problem. SWD is associated with decreased alertness, higher risk of work-related accidents, and increased depression and anxiety. SWD is also associated with metabolic changes increasing the risk of heart disease, obesity, and digestive problems caused by irregular eating habits or poor diet. The following tips can help if you work nontraditional hours:

• Can you... Request to work the same shift several nights in a row, to avoid flipping between day and night shift schedules on consecutive days. This helps to regulate the circadian system.
• Commit to a consistent sleep schedule, darkening the bedroom with blackout shades, and creating a quiet atmosphere as much as possible. You might reduce light exposure even earlier by wearing sunglasses as soon as you leave work. To reduce noise, wear earplugs and use a white noise machine to block sounds.
• After finishing a night shift, try to return home and go to bed as soon as possible. Running errands, watching television, talking with family, or exercising can re-energize your body so that falling asleep becomes more difficult.
• Although it is tempting to run errands and attend medical appointments during the day when places are less crowded, try to minimize doing them immediately after work so that you can return home and honor your sleep schedule.
• Meal Schedule. Do meal planning to ensure that quick easy meals are ready when you arrive home, and bring prepped meals/snacks to work for overnight shifts to prevent reliance on fast food and takeout meals. Try to avoid eating a large meal right before bed, which can increase the risk of reflux and indigestion.

References

1. Murray, MT. Insomnia. Pizzorno J, Murray M. Textbook of natural medicine, 3rd ed. (p.1553). Sydney: Churchill Livingstone Elsevier, 2006.
2. Report to the Sleep Health Foundation 2016 Sleep Health Survey of Australian Adults. Viewed 29 May 2019, https://www.sleephealthfoundation.org.au/pdfs/surveys/SleepHealthFoundation-Survey.pdf
3. Sleep Deprivation and Deficiency. Viewed 29 May 2019, https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency
4. Fatima Y, Doi S & Mamun A. Longitudinal impact of sleep on overweight and obesity in children and adolescents: A systematic review and bias-adjusted meta-analysis. Obesity Reviews 2015; 16(2):137-149.
5. Halgamuge MN. Pineal melatonin level disruption in humans due to electromagnetic fields and ICNIRP limits. Radiat Prot Dosimetry 2013 May; 154(4):405-16.
6. Howatson G, Bell PG, Tallent J, et al. Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. Eur J Nutr 2012 Dec;51(8):909-16.
7. Braun L, Cohen M. Herbs and natural supplements, 3rd ed (pp.604, 722, 681-687, 912). Sydney: Churchill Livingstone Elsevier, 2011.
8. Chen J, Liu X, Li Z, et al. A Review of Dietary Ziziphus jujuba Fruit (Jujube): Developing Health Food Supplements for Brain Protection. Evid Based Complement Alternat Med 2017 Jun 7.National Sleep Foundation. How much sleep do we really need? Viewed 18 July 2019,
9. National Sleep Foundation. How much sleep do we really need? Viewed 18 July 2019, https://www.sleepfoundation.org/excessive-sleepiness/support/how-much-sleep-do-we-really-need
10. Mayo Clinic. Human growth horone (HGH): Does it slow ageing? 2016. Viewed 25 July 2019, https://www.mayoclinic.org/healthy-lifestyle/healthy-aging/in-depth/growth-hormone/art-20045735

Links:
https://medlineplus.gov/ency/patientinstructions/000871.htm. 
https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency. 
https://www.cdc.gov/niosh/emres/longhourstraining/clock.html.
https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx.
https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/understanding-Sleep. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5353813/. 
https://www.ncbi.nlm.nih.gov/books/NBK19956/. 
https://aasm.org/resources/pdf/pressroom/adult-sleep-duration-consensus.pdf

https://www.cdc.gov/sleep/features/getting-enough-sleep.html. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4651462/. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768102/
https://www.cdc.gov/features/sleep-heart-health/index.html. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767932/. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5634544/.
https://www.nhlbi.nih.gov/files/docs/public/sleep/healthy_sleep_atglance.pdf
https://medlineplus.gov/alcohol.html. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4440346/.