Sleep Physiology — Sleep Series Part 2

Sleep Physiology — Part 2 of Sleep Series

Sleep Physiology — Part 2 of Sleep Series

Sleep Stats and General Information – Sleep Series Part 1

What makes us fall asleep?

This is an important question because if we know what factors contribute to our drive to sleep the we can know how to get better sleep. Our inclination to sleep is not as simple as it seems. There are multiple driving factors relating to both circadian rhythms of the body and metabolic factors. Metabolic fatigue in your brain, sleep physiology, and its drive to make you want to sleep increases with number of hours awake.

Basically, when your brain is on, it uses energy and the process of using energy creates wastes that slow thinking and make you sleepy. The more energy your brain has expended thinking, problem solving, dealing with stress, the more wastes build up, the more tired you feel (Lorenzo 1995). This is a big contributing factor to feeling sleep initially – thinking is harder and your eyes feel heavy. Although this might be what drives you to put your jammies on, it’s actually the circadian rhythms of your body that will keep you asleep and determine the quality of your sleep.

Fluctuations and Sleep Physiology

Circadian rhythm drivers of sleep include melatonin and body temperature. Most people don’t realize that your body temperature fluctuates throughout the day and it’s a very important factor in your sleep quality. It’s like what happens during hibernation. Essentially our body temperature dips until about 6am. The lower body temperature promotes slow wave sleep. This is critical for clearing wastes from your brain promoting cognitive function the next day (Lazar et al. 2015). Getting enough hours before 6am is critical for getting enough slow wave sleep for optimal brain function – 6-8 hours before 6am is ideal (that means getting to sleep before midnight).

As you get older the core temperature fluctuations change such that your body temperature rises earlier in the night – this is why older people tend to wake up earlier and why some older people have a hard time getting restful sleep, as slow wave sleep is impaired (Dijk et al. 2000).

Fluctuation of Melatonin

Lastly, the daily fluctuation of melatonin is one of them most important factors in our sleep timing and quality. It is released from the brain in a way that follows the pattern of the sun rising and setting because its release is inhibited by light. This means that it is low during the day when the sun is up, and higher at night when the sun sets. It also means that our habits and dependence on artificial light can interfere with melatonin production, impairing sleep onset and quality (Lazar et al. 2015). This is extremely important because melatonin promotes the release of anabolic hormones (building and repair hormones). Furthermore it is an anti-oxidant, and inhibits inflammation and catabolic hormones.

For this reason, it’s critical for maintaining a healthy body and is especially important in growing bodies and a body in repair (i.e. post-injury, post-surgery, post-exercise). It’s also important for the formation of new neural networks that turn short-term memories into long-term memories (i.e. learning). The long and short of it is that melatonin is very important for sleep quality and the effects that our sleep habits have on our physical and mental health and function.

Measuring Sleep Patterns

Sleep phases are generally evaluated by polysomnography – a combination of brain activity, eye movement, and muscle activity. Brain activity is measured by wavelength using encephalography (EEG), while eye movement and muscle activation are measured by electroculography (EOG) and electromyography (EMG), respectively. Using these measures, sleep can be characterized as rapid eye movement sleep (REM) or non-rapid eye movement sleep (NREM). NREM is further separated into stages 1-4, with 1 being very light sleep and 3-4 being very deep sleep – the respective characteristics are given in greater detail in figure 1.

Sleep Physiology — Part 2 of Sleep Series

Figure 1. Characteristics of REM and NREM stages 1-4 sleep by EEG, EMG, and EOG.

Notable Phases of Sleep

REM sleep – REM occurs perfominantly in the end of the night, and is characterized by high activity on EOG and EEG, and very low activity on EMG. It is critical for learning and memory consolidation and is sensitive to melatonin concentrations. A common concern among sleep scientists and medical professional is the effect of electronics on REM sleep. Blue light from electronics suppresses melatonin released from the brain, which is thought to impair REM sleep quality and therefore may effect learning.

Melatonin also inhibits cortisol release, so these hormones fluctuate throughout the day/night inversely (when melatonin is high, cortisol is low and vice versa) (Reidner et al. 2007). This is important because cortisol is a stress hormone and, while it has some important functions, if it is allowed to stay high all the time, it can contribute to the development fo stress related illness. It’s also why sleep is extra important during times of stress.

REM Sleep is Critical During Periods of Learning and Training.

Slow Wave Sleep – SWS is restorative and important for promoting rest and recovery of your brain and your vital organs. Our organs are controlled by our involuntary autonomic nervous system. This system has two arms: the sympathetic system is activating, while the parasympathetic system is relaxing. SWS decreases sympathetic activity. This allows our vital organs to rest and recover (they are on all day, after all!). SWS is also critical for brain recovery and clearing wastes to promote optimal cognitive function in the morning.

SWS is Critical When Next day Performance is Important.

Sleep Physiology — Part 2 of Sleep Series

Sleep Physiology — Part 2 of Sleep SeriesC

Sleep Physiology — Part 2 of Sleep Series

Figure 2A – Proportion of time during sleep that is spent in the respective phases of sleep. Figure 2B – The timing of respective sleep phases. More time is spent in slow wave sleep at the beginning of the night. In contrast, REM sleep occurs predominantly towards the end of the night.

(adsbygoogle = window.adsbygoogle || []).push({});
You Might Like:

Family outdoors

Stop Taking Loans on Your Health

Over the last few years “hustle” culture has embedded itself into the lives of people across the globe. However, while the drive to work yourself to the bone in your twenties, thirties, and forties to...
Box squats

What Is the Most Effective Squat Position?

Squats are often described as the king of all exercises – and for good reason too. They not only train all the muscles of the lower body, but they also work the muscles of the...

Habit Stacking: How to Build Exercise Habits

Changing your routine to adopt better lifestyle behaviours can have a profound impact on your health and fitness. It is also something that most people find extremely difficult. Which is why we are always on...

Dijk DJDuffy JFCzeisler CA. (2000) Contribution of circadian physiology and sleep homeostasis to age-related changes in human sleep. Chronobiol Int., 17(3):285-311.

Lazar ASLazar ZIDijk DJ. (2015) Circadian regulation of slow waves in human sleep: Topographical aspects. Neuroimage, 116:123-34.

Lorenzo IRamos JArce CGuevara MACorsi-Cabrera M. (1995) Effect of total sleep deprivation on reaction time and waking EEG activity in man. Sleep,18(5):346-54.

Riedner BAVyazovskiy VVHuber RMassimini MEsser SMurphy MTononi G. (2007)

Sleep homeostasis and cortical synchronization: III. A high-density EEG study of sleep slow waves in humans. Sleep, 30(12):1643-57.

(adsbygoogle = window.adsbygoogle || []).push({});


Best Time to Work Out Based on Sleep Animal

picture of someone sleeping in a bed

Is Sleep the Missing Link to Athletic Performance?

woman walking

The Effects of Sleep Quality and HIIT


Melatonin for Sleep: is it Safe?

Sleep Naked

5 Benefits of Sleeping Naked: The Scientific Facts

best sleep aids

Best Sleep Aids

Best essential oils for sleeping

6 Best Essential Oils for Sleeping

OTC sleeping pills

Best OTC Sleeping Pills

Best Sleep Trackers

6 Best Sleep Trackers

5 Best Sleep Apps

5 Best Sleep Apps

Leave a Reply