Stage Three Sleep
Some scientists consider stage 3 and 4 to be one stage. Your body rests during these stages to help cells recover. Your cells produce the most growth hormone here to mend your bones and muscles.
While all this is happening, your muscles are fully relaxed. Mental activity is limited, including dreaming.
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Rapid Eye Movement or REM follows after the four stages of NREM (non-REM) sleep and occupies about one-fifth of total rest time in adults.
During REM, all vivid dreaming takes place. Our internal temperature is at its lowest. Our heart rate increases and our breathing is irregular. Generally, our muscles are immobilized, and we are incapable of physical response, except for our eyes and ears. However, our brain is fully active.
When we fall asleep, the nearly 86 billion neurons in our brain starts to fire evenly and rhythmically. Our sensory receptors become muffled at the same time.
The first stage of shallow sleep lasts for about 5 minutes.
Thomas Edison said that sleep is "a bad habit." Like Edison, we seem to think of sleep as an adversary and try to fight it at every turn. The average American sleeps less than the recommended seven hours per night, mostly due to electric lights, television, computers, and smartphones.
However, we are ignoring the intricate journey we're designed to take when we sleep.
Our molecular clock inside our cells aims to keep us in sync with the sun.
When we disregard this circadian rhythm, we are at a greater risk for illnesses such as diabetes, heart disease, and dementia.
- The prefrontal cortex, the place in the brain that controls decision-making and problem-solving, is the first to suffer from not enough sleep. It causes you to be more irritable, moody and irrational.
- Sleeping less than six hours a night increases the risk of depression, psychosis, and stroke.
- Lack of sleep is tied to obesity. The stomach and other organs overproduce ghrelin, the hunger hormone, which causes overeating.
- More than 80 million American adults suffer from chronic sleep deprivation.
- Fatigue contributes to more than a million auto accidents each year.
- About one-third of us will suffer from some form of sleep disorder.
- People with Kleine-Levin syndrome will sleep nearly nonstop for a week or two and return to regular cycles without any side effects.
- 4 % of US adults take sleeping pills in any given month.
We spend about half our sleeping time in stage 2. It can last up to 50 minutes during the first 90-minute sleep cycle, and less during subsequent cycles.
During this time the brain consolidates the information that has been collected during the waking hours. It makes connections you might not make otherwise. It also curates which memories to keep and which to delete.
We can remain in stage 4 - similar to a coma or brain death - for only about 30 minutes before the brain wakes up and falls back to sleep again.
Even healthy sleepers wake several times a night, but might not be aware of it.
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Your dreams may be ways of confronting emotional dramas in your life.
Because your brain is operating at a much more emotional level than when you’re awake, your brain may make connections regarding your feelings that your conscious self wouldn’t make.
- Scientists study activity in the brain with a tool called electroencephalography ( EEG), that measures electrical signals coming from neurons.
- The brain is not turned off while you sleep - there is a lot of activity going on, even if you’re not aware of it. You cycle through four different sleep stages, and each shows up as a different pattern on the EEG.
- Each sleep stage is also associated with different patterns of chemicals in your brain (neurochemicals - the way brain cells use to communicate with each other).
Adults and babies alike dream for around two hours per night—even those of us who claim not to.
Researchers have found that people usually have several dreams each night, each one typically lasting for between five to 20 minutes.
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