 Sleep accounts for one quarter to one third of the human lifespan, but have you ever wondered what exactly happens when you sleep? Do you assume that the only part of your body that functions are your eyes when you close them and open them? John Hopkins sleep expert and neurologist Mark Wu, MD. PhD once asserted that before the 1950s, most people believed that sleep was a passive activity during which the body and brain were dormant. However, it has been discovered that sleep is a period during which the brain is engaged in various stages and several activities necessary to live which are closely linked to the quality of life. In this video, I will be showing you what happens when you sleep. I will first explain the different stages of sleep and I will further specify some of the activities that take place during the stages. If you are new here, consider subscribing to this channel for more awesome videos such as this one. Sleep can be divided into two broad stages, non-rapid eye movement and REM and rapid eye movement, REM sleep. The vast majority of our sleep, around 75 to 80%, is REM. Electrical structures characterize the stage in the brain, known as sleep spindles and high slow delta waves. This is the time we sleep the deepest. Every individual begins to night in non-REM sleep and spends most of their rest time there. Sleep starts basically with drowsiness, then proceeds into a light sleep in the N1 stage and then most of the deep N3 stage. During this secession, your brain becomes less responsive to the outside world and it gets harder to wake up. Your thoughts and most body functions slow down. You spend about half a regular night's sleep in the N2 phase when scientists think you fall away long term memories. During the night, you cycle through five separate stages of sleep, every 90 to 110 minutes experiencing between three and five dream periods each night. The five stages of sleep can be differentiated by chances in the electrical activity in your brain, measured by electron's phallogram, EEG. The first stage begins with drowsiness as he drifts in and out of consciousness and is followed by light sleep and then by two stages of deep sleep, N2 and N3. Finally, your brain perks up again. Resuming activity that looks much more like wakefulness and you enter rapid eye movement, REM sleep, the time that your most vivid dreams occur. This cycle happens several times throughout the night and each time the period of REM sleep grows longer. Here are some of the other activities that occur during this time. 1. Your brain processes information gathered during the day. What do you think happens to your brain when you sleep? Do you think it stops working? Well, don't be misled into thinking that when you're asleep, your brain has shut off too. Your mind is quite busy while you sleep, sorting and storing information from the day. This process is particularly essential for creating long-term memories as your brain merges all the information it has picked up during the day and fouls it away for later use. Contrary to the view of others and even scientists, you are not unconscious when you sleep instead. During sleep, your mind goes into the subconscious state. An article on operation meditation stated that, in fact, the subconscious mind works fast when we are not alert, for instance, while sleeping. So if your brain processes information during sleep, although you may seem or even get close to unconsciousness, you are not unconscious. 2. Information is cleared. Clearing of information is what scientists have presumed that the REM stage does. It helps your brain clear out the information you don't need. This is the reason why people who take a look at the challenging puzzles sub it more quickly after the sleep than before and they remember facts and tax better too. Those deprived of REM in particular compared with other sleep stages lose disadvantage. According to the discoveries of researchers at Boston University in Massachusetts, during sleep, the fluid present in the brain and spinal cord, called the cerebrospinal fluid, washes in and out like waves, helping the brain get rid of accumulated metabolic trash. Thus, it was concluded that sleep is essential, not just in terms of allowing the mind to actualize, but also making space for cleaning processes to take place. However, many of the mechanisms through which this clearing out of the brainwaste takes place during sleep are yet to be recognized. 3. Your muscles paralyzed. As earlier said, while asleep, you cycle through periods of non-rapid eye movement sleep and REM and rapid eye movement sleep, REM. Studies have proven that it is during REM sleep that we have the most vivid dreams during REM sleep. The brainstem is said to communicate with the hypothalamus and other brain structure to help you drift off and wake up. Together, they make a chemical called GABA that quiets arousal centers that might keep you from sleeping. The brainstem also sends signals to temporarily paralyzed muscles that move your body, arms and legs, which means that you cannot move. Some scientists believe that this might be so that you don't physically act out your dreams. The paralysis of the muscles stops you from acting out your dreams. 4. Your immune system releases inflammation fighting cytokines while you're sleeping. Your immune system releases a type of small proteins called cytokines. If you're sick or injured, these cytokines help your body fight inflammation, infection and trauma. Without enough sleep, your immune systems might not be able to function at its best. During deep sleep, your body works to mend organs and other cells. Chemicals that enhance your immune system begin to circulate in your blood. You consume about a fifth of your night sleep in deep sleep when you're young and more if you haven't slept enough. But as you age, that time starts to fade and by the time you're over 65 it could be down to zero. This may be the reason why you are more robust and healthier when you're young. 5. Your body temperature decreases. As bedtime approaches, your body temperature starts to fall. Paving the way for a good night sleep, your body also tends to lose heat which helps you fall and stay asleep. That's one of the reasons experts say you should exercise close to bed time, exercise heats you and we sleep better when we're calmer. Your temperature which drops a couple of degrees at the state of drowsiness is lowest about two hours before you wake up. Studies have shown that in REM sleep, your brain even turns off your body thermometer. That's when the heat or cold in your bedroom affects you more. In general, a cooler room helps you sleep better. A few push-ups or a jog when you wake raises your temperature and makes you more alert. 6. Dreams. Though many scientists and even religionists have talked about your dreams for thousands of years, they are still a mystery in many ways. It is still not clear what causes them, but they are a vital part of our sleep. Dreams are most common during REM, especially when they are very visual, but you can dream in other sleep stages as well. However, nightmares when people appear to be awake and cry out in fear or panic happens in deeper states of sleep. 7. Your body makes more some hormones when you're asleep and lowers others. For instance, when you sleep, levels of growth hormone go up and cortisol which is tied to stress goes down. Some scientists think insomnia could be related to a problem with your body's hormone making system. Also, a lack of sleep can mess with degrees of hormones that control hunger, leptin and ghrelin and that can change how much you eat and make you gain weight. 8. Anti-diuretic hormone, ADH, helps you not to have to pee. Have you ever wondered why you have to go to the toilet to pee every couple of hours during the day, but can sleep a whole eight without heading to the loo? Thanks to ADH, an anti-diuretic hormone released by the brain under a circadian rhythm which turns out the need to urinate so often at night. Usually, the amount of ADH in the body is higher during the night, but if the levels of ADH remain low during the night, the body will produce large amounts of urine, so urination during the night is also likely. 9. Your sympathetic nervous system relaxes. During sleep, your sympathetic nervous system, which controls your fight or flight response, gets a chance to unwind. Studies have shown that when an individual is deprived of sleep, sympathetic nervous system activity increases, which is also mirrored by a rise in blood pressure. Scientists studying coronary disease are investigating whether there is a relationship between decreased sleep duration and increased risk of heart disease. Your body does a lot of important work when you are asleep. Adequate sleep is vital for your physical and mental health, so you must endeavor to make good sleep a priority.