Understand: The Sleep Cycle

Most of you think sleep is simply a time when the brain and body “shut off” for few hours to rest and prepare for the next day. Fun fact: Neither your body nor your brain shuts down when you fall asleep. The human body in preparation for the next day. But to understand, neither the body nor the brain “shut down” when we sleep. The human body follows the circadian rhythm. This is a natural pattern that is influenced by the environment and the genes to determine your sleep patterns. It releases hormones when it’s time to sleep. Abnormalities in the circadian rhythm can lead to sleep disorders like insomnia and many other. 

Good quality sleep is very important for your daily routine - you spend about ⅓ of your time doing it. Without sleep, you cannot maintain the pathways in your brain that let you learn and create new memories and it’s harder to concentrate and respond quickly. 

A lot is going on inside your head while you’re in a slumber. Scientists have studied these changes through electroencephalography and have demonstrated that sleep progresses through a series of stages in which different brain wave patterns are displayed. 

There are two basic types of sleep: rapid eye movement ( REM) sleep and non-REM sleep ( which has four different stages). Each is associated to particular brain waves and neuronal activity. Your system cycles through all stages of non-REM and REM sleep several times during a typical night.

Usually, a person would begin a sleep cycle every 90-120 minutes resulting in four to five cycles per sleep time. 

Stage 1 Sleep

Stage 1 is known as the light sleep stage as it lasrs for about 5-10 minutes on an average. In this stage, the mind and body begin to slow down making you to feel drowsy and relaxed. Light sleep is also when it’s easiest to wake up. Occasionally people may experience hypnic jerks or abrupt muscle spasms and may get a sensation of falling (hypnic myoclonia).  

Stage 2 Sleep

According to American Sleep Foundation, people spend 50% of their total sleep in this stage. During this stage, the body temperature and heart rate begin to slow,  the brain produces sudden increases in brain wave frequency known as sleep spindles. Then brain waves slow down. 

Stage 3 and 4 Sleep - Deep Sleep 

Stage 3 and 4 sleep are progressively deeper stages of sleep as the brain begins producing slower delta waves. Stage three lasts for about 30 minutes, while Stage four usually goes on for 45 minutes to an hour. At this point, the muscles of the body are fully relaxed (no moment), breathing rate, blood pressure and body temperature all decrease significantly. Also, the body becomes less responsive to the outside stimuli making it difficult to be awakened. In this stage the body also repairs muscles and tissues, stimulates growth, boosts immune function and build energy for the next day.

REM Sleep 

You generally enter REM sleep about 90 minutes after falling asleep. During this stage, your brain becomes more productive, your eyes have rapid side-to-side movement behind closed lids, your arm and leg muscles become temporarily paralyzed which prevents you from acting out your dreams, breathing becomes faster and irregular and your heart rate and blood pressure increases to near waking levels. Most of your dreaming occurs during REM sleep, although some can occur in non-REM sleep too. Awakening and arousal can occur more easily in REM as the brain is active but it can also leave you feeling dizzy and overly sleepy. 

Our brain consolidates and processes information from the day before to store in the long term memory during REM Sleep. This play a crucial role in learning and memory function too.  

The sequence of the sleep cycle 

It is important to know that sleep does not progress through these stages in sequence. The sleep cycle begins with stage 1 and progresses into stages 2 and 3. After stage 3 sleep, stage 2 sleep is repeated before entering REM sleep. Once REM sleep is over, the body can return to any stage based on body’s requirement.

On average, you enter the REM stage approximately 90 minutes after falling asleep. The first cycle of REM sleep might last only a short amount of time but with each cycle, it becomes longer. As our sleep progressesm REM sleep can last up to an hour. 

Note: As we age, the timing and duration of our sleep cycles change. Older individuals tend to experience a much longer sleep cycle with less time in REM as opposed to infants who experience shorter cycles with more REM sleep. It’s almost like all the meetings, exhausting commutes, and stressful to-do lists fade away as you sail into nocturnal bliss.