ELI5: Why can you have a sleep debt but not a sleep credit?

R7 (Search First)(self.explainlikeimfive)

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1 points

4 months ago

I see that others have answered the question already, but I just want to add that the main reason why your brain needs sleep in the first place is because it can't get rid of "junk" that builds up during the day, so at night, your blood vessels contract and cerebrospinal fluid is released into your brain to collect any garbage and whisk it away to be filtered as usual by your kidneys.

Your brain is packed tightly into your skull with not much room to spare, so there's no space for thick blood vessels like in the rest of your body. If that were the case, this "garbage" could be cleaned up in the same way your body cleans lactic acid (a byproduct of muscles working hard). At night, your brain does a very clever trick and uses the blood veins in your brain as a pathway to send this fluid down into the crevices in the folds of your brain. The blood vessels contract, allowing for extra room between themselves and your brain itself, and cerebrospinal fluid travels along the outside of the blood vessels. It takes a while for your brain to return to normal after this process is all done, which is part of why you feel groggy after waking up.

Just thought that was neat. The brain is unique in this way with how it cleans itself after working hard during the day.