Sleep cycle

Sleep cycles refer to the stages of sleep an individual goes through during a typical night's rest. Sleep is not a uniform state; rather, it consists of various stages that occur in a cyclical pattern. Each sleep cycle typically lasts for about 90 to 120 minutes and includes both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep stages.

Stages of sleep

• There are four stages of sleep, divided into NREM and REM sleep:
• NREM sleep:
• Stage 1 sleep: The transition period between wakefulness and sleep, which lasts for about 5-10 minutes. During this stage, the body begins to relax, and brain waves shift from alpha waves to slower theta waves.
• Stage 2 sleep: This stage makes up approximately 45-55% of an adult's sleep and is characterized by further relaxation, a drop in body temperature, and slowed heart rate. Brain waves continue to slow down, with occasional bursts of rapid waves called sleep spindles.
• Stage 3 sleep: Also known as slow-wave sleep or deep sleep, this stage is essential for physical restoration and the consolidation of memories. The brain produces slow delta waves, and it is more difficult to awaken someone during this stage. This stage typically makes up about 20-25% of an adult's sleep.
• REM sleep:
• Stage 4 sleep: REM sleep is characterized by rapid eye movements, increased brain activity, and vivid dreaming. During this stage, the body's muscles are temporarily paralyzed to prevent physical movement during dreams. REM sleep typically makes up about 20-25% of an adult's sleep and becomes longer and more frequent as the night progresses.

Sleep cycles throughout the night

• Throughout the night, an individual goes through several sleep cycles, each lasting around 90 to 120 minutes. The first cycle usually contains a shorter REM stage, while later cycles have longer REM stages. As the night progresses, the amount of time spent in deep sleep (N3) decreases, and the time spent in REM sleep increases.
• A full night's sleep typically consists of four to six sleep cycles. Getting an adequate amount of both NREM and REM sleep is crucial for overall health, as each stage plays a vital role in physical and mental restoration.

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  Diagram of a typical sleep cycle
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  Illustration of the stages of sleep
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  Asian elephant sleeping