The Stages of Sleep: A Detailed Overview
We spend up to a third of our life asleep, yet the process of sleeping and all its intricacies are still unknown. For centuries, the stages of sleep have puzzled scientists and continue to hold secrets. Sleep is an enigmatic process that can vary with age, culture, and individual. A comprehensive overview of the sleep process provides much insight and can inform health and lifestyle decisions.
Sleep occurs in several stages, progressions, and cycles. It begins with a light stage of sleep, known as NREM (non-rapid eye movement) sleep, and continues with a deep stage of sleep, known as REM (rapid eye movement) sleep. REM sleep is often seen as the most restful stage, as it is necessary to the learning and memory processing functions of the brain. During the night, sleep progresses through the stages in four or five cycles. Most adults require between seven to nine hours of sleep per night to feel most rested.
In order to understand the importance and effectiveness of sleep, it is necessary to become familiar with the process for each sleep stage.
Stage 1 Sleep: NREM
The first stage of sleep, NREM, is a light sleep that allows the body to transition from wakefulness into a the sleep state. Helping to initiate this stage are hormones which cause the body to slow down and release tension. It is known as light sleep, and is the stage in which one is able to be easily awoken. This stage of sleep is brief and is the beginning of the first sleep cycle.
Most adults spend roughly five to ten minutes in this sleep stage.
Stage 2 Sleep: NREM
Stage two is the second stage of the NREM sleep cycle and is considered a light sleep as well. This is the stage in which the body further relaxes, the heart rate and breathing slows, and the body temperature decreases. It is also the stage in which the brain produces short bursts of brain waves known as sleep spindles.
This is a slightly deeper stage of sleep, however one can still be woken from this stage easily. Adults spend approximately half of the total sleep time in this sleep stage, usually lasting between 20-60 minutes.
Stage two can be further divided into two parts: 2A and 2B.
Stage 3 Sleep: NREM
Stage three is the deepest stage in the NREM sleep cycle. This is the stage in which the brain produces delta level waves. These are the slowest waves but are also the most powerful. This is the stage in which hard to wake up, and often it takes some time to wake up and adjust into a state of alertness.
Stage three sleep is helpful for the body to recuperate and recharge, as this is the stage that stimulates the body’s repair and maintenance processes. Adults spend on average 15-20% of total sleep time in this stage.
Stage 4 & 5 Sleep: REM
- Stage four is the first stage of the REM cycle.
- Stage five is the second stage of the REM cycle.
- REM sleep is the most restorative stage and is crucial for learning and memory processing
- Moods may affect the REM cycle; for example, those with depression may have a longer REM sleep cycle.
- In general, adults spend 25-30% of total sleep time in a REM sleep.
The Process of Transitioning Through Stages of Sleep
The cycle begins with NREM sleep and gradually transitions to REM sleep before repeating the cycle. This cycle usually takes between 90-120 minutes to complete. Different sleep needs require a different length of time to cycle through the various stages of sleep; in adults, a shorter cycle is associated with better sleep. It is important to be mindful of one’s sleep cycle in order to establish good sleep patterns.
Conclusion
Understanding the stages of sleep can help inform proper sleep hygiene and promote good health. Becoming familiar with the different stages of sleep and their related functions can be the first step to achieving restful sleep.