WHY DO WE NEED TO SLEEP?
There are many good answers to this question, but one of them is – we need brain wash!
This is taken care of by the GLYMPHATIC system, an amazing system that – during sleep (especially deep sleep) – helps the brain to get rid of cellular waste, that could otherwise clot up the brain and ultimately lead to dementia (e.g. Alzheimers disease).
The brain is a very dense network of both neurons (nerve cells) and glia cells (support cells). During wakefulness, cellular waste builds up, just like when our daily activities generate waste. However, the activity is too high – and the space too limited – to wash away the waste. When we fall asleep, nerve cells change their activity and the support cells named astrocytes shrink in size and leave more space. This opens up for fluid coming from the so-called perivascular space (described in film), which then can flow into the cell-dense areas. The flow goes from arteries to veins and washes out cellular waste products so that we can wake up refreshed and ready for new activities.
An analogy could be garbage trucks, that cannot work during the day because of heavy traffic and activity. But at nigth, the activity and traffic ceases and waste can be picked up and removed.
The system was described and named by the Danish scientist Maiken Nedergaard in 2013 (watch a full talk with her from the Europhysiology conference in 2018, describing the system in detail here: https://youtu.be/He6HMnMbxAc).
Scientific references in the end of the film.