Check out the Narcolepsy Chats at: TalkAboutSleep.com Chats every Mon & Thurs (check schedule for any changes)
Sleep Cycle
by Bulldawg (no login)
Sleep Cycle
Sleep is a physical and mental resting state in which a person becomes relatively inactive and unaware of the environment. Studies have shown that the brain is as active during sleep as it is when awake. Throughout an eight-hour sleep cycle, a normal adult alternates between two very different states, non-REM and REM (Rapid Eye Movement) sleep.
Sleep is characterized by two distinct states, non-REM sleep and REM sleep. Non-REM and REM sleep alternate in 90- to 110-minute cycles. A normal sleep pattern has 4-5 cycles.
The five-step sleep cycle repeats itself throughout a night of sleeping, much like a roller coaster. As a person drifts off, Stage 1 begins. After a few minutes, the EEG detects sleep. It may take anywhere from 30 – 40 minutes to cycle through Stage 2 through 4. Now, an individual backtracks through Stage 3, then Stage 2, and finally into REM sleep. This occurs 4 - 5 times per nigh
Stage 1
This stage could be termed the "dozing" stage. Only 5% of non-REM sleep is spent in Stage 1. It is the transitional period of very light sleep.
Stage 2
This stage is often considered the official onset of consolidated sleep. Approximately 45% of non-REM sleep is spent in Stage 2. Stage 2 Sleep is characterized by a lack of eye movements,
Stage 3
As sleep advances progressively deeper, an individual becomes difficult to arouse. A person spends approximately 12% of non-REM sleep in this stage.
Stage 4
Stage 4 is characterized by very deep sleep. Of the roughly 75% of non-REM sleep, approximately 13% is spent in this final stage. A person in one of the two latter stages, either 3 or 4, is harder to wake than a person in Stage 1 or 2. People who wake during deep sleep often feel groggy and disoriented for several minutes
Stage 5
Most dreaming takes place during REM (Rapid Eye Movement) sleep. Periodic eyelid fluttering, muscle paralysis, and irregular breathing, body temperature, heart rate, and blood pressure distinguish REM from non-REM sleep stages. REM sleep is also called "paradoxical" sleep because brain wave activity is similar to an awakened state. It is during REM sleep that the brain blocks signals to the muscles to remain immobile so dreams will not be acted out. Adults spend about 20 - 25% of their sleep cycle in REM sleep.
A major reason why humans sleep is due to circadian rhythms, also known as the biological clock. A cycle that lasts 24 hours is called circadian. Some physiological functions that are circadian include body temperature and certain hormone secretions. Through a complex process of hormonal and neurological changes, daylight naturally triggers periods of wakefulness. Studies have shown, however, that the absence of light does not disable our biological clocks.
In narcolepsy, however, you suddenly fall into REM sleep without first experiencing NREM sleep and at abnormal times, such as during the day. Also, some of the aspects of sleep that normally occur only during REM sleep, such as sudden lack of muscle tone, sleep paralysis and vivid dreams, occur at other times during sleep in people with narcolepsy.
Scientists believe that people with narcolepsy who begin to feel drowsy and then drop instantly into "dream sleep" may have imbalances in certain brain chemicals important in regulating sleep.