Why Do We Need Sleep?

It's a simple question, yet the answer is still unclear.We spend 1/3 of our lives sleeping, therefore this physiological process must be very important for our overall health.Did you know that you can literally die of insomnia after 1 week but you can sustain 2 months without eating? pretty impressive right? Although some subjects reported longer periods of non-sleep including Randy Gardner, the holder of Guinness world record for the longest period a human has intentionally gone without sleep and not using stimulants of any kind, he stayed awake for 11 days and 25 minutes!

That's not the end of the story, some other subjects claimed that they never slept a minute in their entire life.To understand the phenomenon better we should first understand the physiological basis of sleep.

About 15% of our genome contains information related to the circadian rhythm.On on hand, both external and internal influences regulate the expression of these genes such as light exposure and previous sleep time.On the other hand, sleep cycles are synchronized by the interaction of different parts of the brain including.

The Pineal Gland: A small region located within the brain’s two hemispheres that produce a hormone called Melatonin which regulates the day-night cycles.

Throughout the day, melatonin levels rise gradually until a maximum between 00 and 07 AM when we are fully asleep.Also, the exposure to light decreases indeed melatonin production and this phenomenon are evident in blue light exposure from electronics after staying online all night.It's important to notice that melatonin is the main cause of circadian rhythm regulation in blind people.

In animals, melatonin is also involved in seasonal changes and reproduction, that's why animals like bears and ants know when winter is coming.

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Suprachiasmatic nucleus: A group of cells located in the hypothalamus (pituitary gland), they receive visual signals from the retina via the optic nerve and regulate behavioral rhythm.It can affect directly melatonin production either by inhibition of the pineal gland or increasing excitatory neurotransmitters production AKA increasing the overall arousal.

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The Brain Stem: it includes 3 different structures called the pons, medulla, and midbrain.Brain stem works synergically with the hypothalamus, it induces sleep by increasing the neurotransmitter GABA.GABA is the main inhibitory neurotransmitter of the mammals' nervous system, it reduces overall stimulation and sends signals to relax muscles essential for body posture and limb movements avoiding any supplementary moves while we sleep.

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The Thalamus: It's the masterpiece simply because it connects all the different parts together.It can be active sending a load of stimulation and you get dreams or quite and you have a good night sleep.

Other parts include the amygdala and The basal forebrain.Adenosine is a waste product of ATP consumption from cells in the basal forebrain, it's the main cause of fatigue accumulation as we stay awake and its receptors are the main target of caffeine.

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By now, you probably have a good idea about the physiology of sleep cycles, but why all of this is important? why we sleep in the first place? Well, I hate to break it to you but there's no definitive answer to this question, luckily many studies were made and the progress was astonishing and scientists believe in different theories.

The most popular one is the restorative theory, in fact, many scientists believe that sleep provides an opportunity for the body to repair and rejuvenate itself.During sleep the majority of anabolic workout is done, this is viewed in both humans and other animals by a release of the Growth hormone during sleep, this is why babies tend to sleep longer hours.

Also, athletes need more sleep than average because of the muscle building, besides this theory is further supported by the build-up of adenosine that I've talked about as the body has a chance to clear adenosine from the system until you wake up.scientists believe that the sleep debt can be quantified by the buildup of adenosine, this hypothesis is the most satisfying one.

From an evolutionary prospect, the inactivity theory suggests that sleeping is a survival mechanism and works by keeping organisms out of harm’s way at the night, especially since they didn't develop the tools to adapt in the dark.Based on this theory, dark is a disadvantage for many organisms and this behavioral strategy presumably evolved to become what we now recognize as sleep.But this theory is unsatisfying because being unconscious is not an advantage after all but rather a disadvantage.

Another theory suggests that we tend to preserve our resources at night.Research has shown that energy metabolism is significantly reduced during sleep up to 10% in humans.During sleep heart rate and respiration decrease, body temperature drop by 0.5 and we go into the vegetative state.For many years natural selection most important feature is competition and in order to sustain a long period of survival, we need energy and energy sources are limited, so our bodies developed a process called sleep for preserving energy during the time when we are inactive=during the night. 

Other theories are still new and under study, but we are fully aware of the benefits of a good night sleep whether we understand it or not.In humans, insomnia leads to impaired memory, reduced cognitive abilities, hallucinations and even death in extreme cases.So make sure to have a good night sleep.

References :   

http://www.bbc.com/news/science-environment-32606341

http://healthysleep.med.harvard.edu/healthy/matters/benefits-of-sleep/why-do-we-sleep

http://www.bbc.co.uk/science/humanbody/sleep/articles/whatissleep.shtml

https://www.livescience.com/32469-why-do-we-sleep.html

https://www.ncbi.nlm.nih.gov/books/NBK11108/

Picture Credit: 

Thumbnail - pixabay.com

All The Rest - wikipedia 

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