Sleep

Quality sleep is as significant to our physiology as food or water. Although we spent one-third of the day sleeping, during sleep, essential physiological processes are happening due to which we can function properly while we are awake. 

 

The importance of sleep

Sleep contributes to the physiological occurrences in the brain, for example, learning and memory consolidation. During the day, new information is taken up and flows to a brain part called the hippocampus, though this compartment serves only as temporary storage. While we are asleep, the brain shuts down from the environmental stimulus then information flows from the hippocampus into the long-term storage of the cortex, where information in brain cells neurons is strengthened through synaptic consolidation (synapses serves as junctions between neurons). In this way, the “space” in the hippocampus is cleared out, and the brain is prepared for new information encoding (Feld and Diekelmann, 2015). Sleep also plays a role in the regulation of emotions and attention – after being awake for more than 16 hours and experiencing sleep deficit, our ability to sustain attention, learn new information drastically drops, the sensitivity to stressors increases (Worley, 2018).

Sleep cycles

Sleep is not uniform, it is divided into 2 main sleep stages – non-rapid eye movement (NREM) and rapid eye movement (REM). Together these stages make up a sleep cycle that approximately lasts 90 minutes and is repeated 4-6 times per night (Suni and Vyas, 2020). There are 4 main sleep phases (NIH, 2019):

      • NREM 1 – this is the first and the shortest stage, lasting only several minutes. In this stage, the breathing, heartbeat, and eye movement slow, muscles relax with occasional twitches, and you can sometimes feel as if you are falling.
      • NREM 2 – a period of light sleep before entering deeper sleep which lasts 10-25 minutes. The body continues to relax even further, body temperature drops, eye movement stops. Around half of the sleep time, you spend at this stage.
      • NREM 3 – deep sleep stage lasting 20-40 minutes. The body is fully relaxed, breathing and heart rate slow to their lowest levels during sleep. You are less responsive to the environment; if awakened at this stage, you can disorientate. It is said that this stage is crucial for regeneration, growth processes, immune system regulation.
      • REM – first reached after 90 minutes of sleep. Eyes move rapidly from side to side, breathing and heart rate become faster. Most dreaming occurs during this stage; however, arm and leg muscles are paralysed – this prevents you from acting out your dreams. We spend 25% of sleep at the REM stage, though with age the time spent at REM sleep decreases.

What makes a good night sleep?

The need for sleep changes with age. Babies sleep as much as 16 to 18 hours a day, children and teenagers on average need 9.5 hours of sleep, while most adults sleep 7-9 hours a night. Older people also need the same 7-9 hours of sleep, but their sleep tends to be shorter, lighter, interrupted by multiple awakenings.

Sleep quality is also affected by the length of each sleep phases, cyclicity of sleep stages, alcohol stress, various sleep disorders, shift work, light, the environment we sleep in and many others.

Tips for getting a good night’s sleep

Although we can not affect our sleep cycle directly, we should pay attention to our sleep hygiene which will help us to pass through sleep phases easier.

      • Set a sleep schedule – go to bed and wake up at the same time every day, even at weekends.
      • Sleep environment – the bedroom should be fairly dark and quiet because light disrupts our circadian rhythm (also known as ‘internal clock’), and it is harder to fall asleep. The temperature in the room should be kept cooler, around 180C.
      • Exercise regularly – you will expend energy and feel sleepier in the evening. WARNING: do not exercise before bedtime as this can disbalance your circadian rhythm.
      • Avoid alcohol, nicotine, coffee before bed, do not overeat – compounds which are stimulants, such as caffeine or nicotine interfere with the release of hormones like melatonin. Meanwhile, alcohol and food can burden digestion because energy is expended to digest stomach content, thus sleep can be fragmented and of lower quality.
      • Do not use electronic devices before bed – smartphones, computers, TV’s emit blue light that also disturbs the circadian rhythm.
      • Do not lie in bed awake. If you can not get back to sleep, read, listen to music, or do something else, until you feel sleepy.

 

Bottom line

Neuroscientist M. Walker once said, doctors should be prescribing sleep itself, but not sleeping pills. Without quality sleep that satisfies all our biological needs, we will not reach our full potential, so you would better sleep tonight! 

 

References

  1. Feld, G.B. and Diekelmann, S. 2015. Sleep smart-optimizing sleep for declarative learning and memory. Frontiers in Psychology. 6(MAY), article no: 622 [no pagination].
  2. Golem, D.L., Martin-Biggers, J.T., Koenings, M.M., Davis, K.F. and Byrd-Bredbenner, C. 2014. An integrative review of sleep for nutrition professionals. Advances in Nutrition. 5(6), pp.742–759.
  3. NIH n.d. Brain Basics: Understanding Sleep. [Accessed 24 May 2021]. Available from: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep.
  4. Suni, E. and Vyas, N. 2020. Stages of Sleep. [Accessed 24 May 2021]. Available from: https://www.sleepfoundation.org/how-sleep-works/stages-of-sleep.
  5. Worley, S.L. 2018. The extraordinary importance of sleep: The detrimental effects of inadequate sleep on health and public safety drive an explosion of sleep research. P and T. 43(12), pp.758–763.
  6. Xie, L., Kang, H., Xu, Q., Chen, M.J., Liao, Y., Thiyagarajan, M., O’Donnell, J., Christensen, D.J., Nicholson, C., Iliff, J.J., Takano, T., Deane, R. and Nedergaard, M. 2013. Sleep drives metabolite clearance from the adult brain. Science. 342(6156), pp.373–377.