Sleep is a naturally recurring state observed in humans and other mammals, birds, reptiles, amphibians, fish, and even insects in some forms. The phenomenon of sleep and the various levels of consciousness involved is somewhat mysterious, and the purposes and mechanisms of sleep are still partially unknown. Sleep involves natural cycles of activity that occur in the brain.
The invention of the electroencephalograph allowed scientists to study sleep in new ways. Sleep progresses through a series of stages in which different brain wave patterns are displayed.
Rapid Eye Movement (REM) sleep
(also known as active sleep or paradoxical sleep)
Non-Rapid Eye Movement (NREM) sleep (also known as quiet sleep), which consists of four stages.
During sleep, the body cycles between non-REM and REM sleep. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. Dreams generally occur in the REM stage of sleep (dreaming sleep) although they can occur in any stage.
The brain also cycles through four types of brain waves, referred to as delta, theta, alpha and beta. Each type of brain wave represents a different speed of oscillating electrical voltages in the brain.
(0 - 4 cycles per second) are the slowest waves and are present in deep, ususally dreamless sleep.
(4 - 7 cycles per second) are present in stage one when we're in light sleep.
(8 - 13 cycles per second) occur during REM or dreaming sleep, and also while we are awake during deep relaxation or meditation.
(13 - 40 cycles per second) are the fastest waves and are present in waking state and usually during physical activity, stressful situations or during strong mental concentration and focus.
These four brain waves make up the electroencephalogram (EEG).
The period of non-REM sleep (NREM) is comprised of Stages 1-4 and lasts from 90-129 minutes (each stage lasing anywhere from 5-15 minutes). Stages 3 and 2 repeat backwards before REM sleep is reached. A normal sleep cycle has this pattern: waking, Stage 1, 2, 3, 4, 3, 2, REM.
In phase one the body is in a transition state between sleeping and waking. In this stage, eyes move more slowly, muscle activity slows down and the body becomes more relaxed. Stage 1 is a light sleep where you can be awakened more easily.
In phase two, eye movement stops and brain waves become slower with an occasional burst of rapid activity. At this point, the body is preparing to enter deep sleep.
In phase three, the body is deeply relaxed. The extremely slow delta brain waves are present and interspersed with smaller, faster theta waves.
In phase four, the body is at its deepest state of relaxation and no eye movement or muscle activity occurs. This is the last stage before REM Sleep. During this stage, the brain produces more delta waves than theta waves.
This is the stage where most vivid dreaming occurs, although dreaming can take place in other stages though typically without recal. The REM sleep phase usually takes place around 90 minutes after initially falling asleep.
In the REM period (Rapid Eye Movement), breathing becomes more rapid, irregular and shallow, eyes move rapidly and limb muscles are temporarily paralyzed. Muscle paralysis is meant to keep the body from acting out the dreams that occur in this stage). Heartbeat may increase and muscles twitches are common.
The very first period of REM sleep typically lasts about 10 minutes, with each recurring REM stage becoming longer in duration, with the final REM phase before awakening lasting about an hour.
All 5 stages of sleep occur in cycles and repeat. The first cycle, which ends after the first REM stage, usually lasts 100 minutes. Each subsequent cycle lasts longer, as its respective REM stage extends. A person may complete five cycles in a typical night’s sleep.
By studying the various altered states of consciousness we can learn more about the mind, and discover how to use our human potential to the fullest. When you sleep, your body rests and restores its energy levels. The active state of sleeping affects both your physical and mental well-being. A good night's sleep can help you cope with stress, solve problems, or recover from illness.
There are a number of factors that can effect the duration and quality of sleep, the sleep cycles and even dreaming, such as: sleep deprivation, irregular sleep schedules, stress, depression or other psychological conditions, environmental factors, illness, foods, drugs and other substances including prescription medications. Humans may also suffer from a number of sleep disorders such as: dyssomnias such as insomnmia, hypersomnia and sleep apnea; the parasomnias such sleepwalking and REM behavior disorder; and the circadian rhythm sleep disorders.
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