Sleep is a state of altered consciousness in which we become less aware of what’s going on around us. Sleep can take different forms in different animals. Dolphins, for example, sleep just half a brain at a time, and can even continue to swim while asleep.
For humans, sleep involves four stages, called N1, N2, N3 and rapid eye movement (REM). N1 is the lightest stage of sleep. It usually occurs right after you fall asleep, and typically lasts less than 10 minutes. During N2, you sink deeper into sleep. This stage is characterised by brief, high-amplitude brainwaves called ‘K-complexes’ and bursts of lower amplitude waves called ‘sleep spindles’. The N3 stage is the deepest stage of sleep, and is characterised by slow brain waves called delta waves. Finally, during REM sleep your brain activity and breathing rate speed up, and your eyes move quickly in lots of directions. Our most vivid dreams tend to occur in REM sleep, and our brain paralyses our muscles so that we’re unable to act them out. During the night, we continually cycle through these four sleep stages, with a full cycle taking around 90 minutes in adults.
HOW MUCH SLEEP DO WE ACTUALLY NEED?
Diese Geschichte stammt aus der October 2020-Ausgabe von BBC Focus - Science & Technology.
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Diese Geschichte stammt aus der October 2020-Ausgabe von BBC Focus - Science & Technology.
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Do We Finally Know How the Egyptian Pyramids Were Built? - A number of breakthrough studies are beginning to paint a picture of how these wonders of the world were built, but much of the story still remains a mystery...
A number of breakthrough studies are beginning to paint a picture of how these wonders of the world were built, but much of the story still remains a mystery...How the Egyptian pyramids were built has long been a mystery. Constructed as tombs for the pharaohs over 4,000 years ago, more than 100 of them remain. The largest one, the Great Pyramid of Giza, was originally 147m tall (482ft). It's made up of about 2.3 million stone blocks, each weighing between 2.5 and 15 tonnes, and would have had to be transported to the building site and lifted into place with techniques available at the time. To put this into context, it's akin to lifting a double-decker London bus to the top of St Pauls Cathedral a few million times.
An Artificial Heart Inspired by Plumbing - Mechanical circulation could revolutionise transplant design and reduce waiting lists
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FOR SOME CREATURES ALIVE TODAY TIME HAS ALMOST STOOD STILL. MEET THE 'LIVING FOSSILS' THAT GIVE US A GLIMPSE INTO LIFE IN THE DISTANT PAST