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As humans fall asleep, body activity slows down. Body temperature, heart rate, breathing rate, and energy use all decrease. Brain waves slow down. The excitatory neurotransmitter acetylcholine becomes less available in the brain. [9] Humans often maneuver to create a thermally friendly environment—for example, by curling up into a ball if cold.
The human organism physically restores itself during sleep, occurring mostly during slow-wave sleep during which body temperature, heart rate, and brain oxygen consumption decrease. In both the brain and body, the reduced rate of metabolism enables countervailing restorative processes. [93]
Sleep can follow a physiological or behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone (possibly with some exceptions; see below regarding the sleep of birds and of aquatic mammals), and a compensatory increase following deprivation of the state, this last known ...
"The mechanisms that rid waste from the brain are far more active when we sleep." When you have healthy sleep, the glymphatic system in your brain—which pumps out waste products—is more active ...
Chronic sleep deprivation (less than 8 hours of sleep) is associated with an increase in body mass index (BMI) and obesity. In a study with 3000 patients, it was found that men and women who sleep less than 5 hours have elevated body mass index (BMI). In another study that followed about 70.000 women for 16 years, there was a significant ...
The study’s first finding is that sleeping between 7 and 9 hours each night was optimal for brain function and boosting cognitive ability. Sleeping less than 7 hours and more than 9 hours ...
During a night of sleep, humans usually experience about four or five periods of REM sleep; they are shorter (~15 min) at the beginning of the night and longer (~25 min) toward the end. Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM.
The human circadian rhythm regulates the human sleep-wake cycle of wakefulness during the day and sleep at night. Ekirch suggests that it is due to the modern use of electric lighting that most modern humans do not practice interrupted sleep, which is a concern for some writers. [18]