Eli5: Why do we need to sleep so much, what happens in the body when asleep that cannot happen while normal resting or relaxing? Or is it just for the brain?
In: Biology
I can’t believe no one is talking about the recent fly study findings.
Basically, fruit flies are a surprisingly good model for human sleep considering they aren’t even mammals.
https://pubmed.ncbi.nlm.nih.gov/18591491/
So, a study was done on them to find a way to keep them alive without sleep, as similarly to humans and many other animals, severe sleep deprivation leads inevitably to death.
They found that just before dying, there was a large build up in toxic compounds in their gut.
More interestingly, they found by neutralising these toxins in the gut, the flies would live normal lifespans without sleep, implying that the cause of death was actually these compounds.
Obviously sleep is still baffling, but I think this is a very interesting step in the direction of figuring out what is going on.
https://news.harvard.edu/gazette/story/2020/06/study-reveals-guts-role-in-causing-death-by-sleep-deprivation/
The best answer I’ve seen is your body actually doesn’t do much different while you sleep but does a lot of things faster such as cell growth. It has to do with how humans use energy – most creatures create energy as it’s needed, for the tasks needed at any given time. More complex systems have more energy demand, but have the benefit of adaptability – a simple creature that only eats algae will only have organs needed to intake and convert algae to energy, and likely will convert it as it’s needed, but will as a result have limited energy for things such as moving quickly away from predators. There does seem to be a link to energy demand and sleep – creatures that perform high intensity activities during their time awake tend to sleep more while slow moving creatures tend to sleep rarely and some never sleep.
The reason we do things such as close our eyes and relax is it allows the body to mostly guarantee that energy that COULD be spent on running, analyzing the environment, so on that COULD be needed immediately won’t happen, so it can safely move energy to body systems for maintenance. Think about a time you had a bad injury – even if it was just a really bad hit to the shin, you are going to feel less energetic. You usually won’t fall asleep though – the body can repair itself while you’re awake but it does it slower.
This is also what is happening when fighters get knocked out – they are more or less going to sleep as the body recognizes the energy demand to repair damage and prevent fatal injury exceeds the availability.
So in short, nothing particularly unique happens while you’re asleep, it’s more like a spaceship rerouting power to systems as they are needed – and by having a period where your body can guarantee with almost certainty you won’t need your full vision, sense of smell, hearing, or muscles, it can slow those systems down and focus on healing. This is also why you may notice if you get a cut in the morning, by night it might look roughly the same, but when you then go to sleep and wake it will appear notably smaller.
We still don’t know. We guess the body needs to repair itself when resting. Remember your muscles grow after you stop exercising, not during. For the brain, learning (remembering things) happens when it rests. Why we need sleep so much is great question: only about 90min of the time we spent in bed is REM sleep.
*I avoid using computer analogy, even thou I love computer/tech. ELI5 is tough*
I only know of several studies relating to the brain that show specifically that sleep is a unique way of resting and metabolic maintenance that cannot be mimicked by other types of rest or sleep. I remembered the studies showed that during sleep the brain is effectively flushed and toxins and built up waste products are removed in that way. This ‘flushing’ did not occur during drug-induced sleep such as with anaesthesia and waste was basically not removed during other states of consciousness.
https://science.sciencemag.org/content/342/6156/373
This is a link to one of those studies.
I’m actually just going to ádrese the part of your question about why we sleep so much.
The fascinating thing is that we don’t actually sleep that much. When you compare the sleep habits of humans vs other mammals, we sleep comparatively little.
As we evolved and developed more complicated social structures that allowed for greater security and the ability to sleep on the ground, we also started having deeper sleep. This means that unlike our tree dwelling relatives or animals that needed to be on high alert to avoid being eaten we could actually get a better rest in less hours.
http://www.bbc.com/earth/story/20160121-the-strangest-thing-about-human-sleep-is-that-we-need-so-little
I learned about this in a neurobiology course I was taking at my university! I’m on my phone right now, but there are a few hypotheses as to why this is. Two are shown below:
* It has been hypothesized that sleep helped us survive. It was seen to be beneficial to sleep at night, since we could not see and our likelihood of getting killed while roaming
* Sleep has been shown to aid in learning and memory cognition. Basically if you learn something and then sleep on it for a bit, you’ll have a better chance of retaining the information.
As pointed out by others: we don’t really know. But think about it: for a prehistoric animal it is really weird to just lie on the ground helpless for several hours when predators could munch you up any time. The payoff has to be immense to justify such a big risk.
I think I read somewhere what was probably a theory that when you sleep, you’re flushing cerebro spinal fluid through your brain and kind of physically self cleaning your brain. That would be in addition to filing all your thoughts and memories.
If you don’t mind a more in depth explanation, the book “Why we sleep” is fantastic. And not too hard to read.
Only thing we do know for a fact is that sleep is so vital that any creature with even a semblance of central nervous system needs sleep and that denying that sleep is fatal.
Maybe it’s just something as simple as that brain cells get tired and need rest or something more complex but we just don’t know for sure, we know the effects but not the cause or reason other similar mystery is why do we and many other creatures see dreams?
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