While finishing the busy work for a day, we always have a strong desire to lie on the bed and to have a sweet dream. Sleep is important to our daily life. By sleeping, our body can take a long break and gain some energy to do the routine of the next day. However, when we lay on the bed, our brain is still working and has some processes to do in the sleeping cycle. But, what is the sleeping cycle and how does it work? The sleeping cycle can be divided into four parts: light sleep, preparing for deep sleep, deep sleep, and REM(rapid eye movement) sleep. 

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     The first stage is light sleep, which occurs when we’ve just gone to bed. We are in the transition between wakefulness and sleep. In this stage of the sleeping cycle, our eyes move slowly. It’s called the non-rapid eye movement (NREM). We feel drowsy. Moreover, can be disturbed easily and cause wakefulness. The body muscle relaxes, moreover, our brain activity becomes slower.  Sometimes, we may experience hypnic jerks, which means feeling like we’re falling suddenly.

 

     The second stage is preparing for deep sleep,which means falling asleep and becomes unaware of the surrounding. Our body temperature starts dropping. The rhythm of the breath, as well as heart rate, begins to slow down. In this stage, we are hard to be disturbed because the sleeping structures include sleep spindles and K complexes which is a waveform that help us not to signal danger when sleeping. (picture 1)These sleep structures serve as protection for the brain from wakefulness, and influence on the quality of sleep. The period of this stage is longer than the other because it comprises approximately 40-60% of total sleep time. 

 

     

 

 

 

 

 

 

 

When entering the third stage, deep sleep, our body muscle totally relaxes and the blood pressure decreases. On the other hand, blood flow to our muscles increases, growth hormones are released, and cells can be repaired. Because of a deep sleep, our body can receive enough restoring hormones from the stresses of a day. This restorative stage often lasts for about 5-15% of total sleep time. Although the period is shorter than the other stages, it’s the most important for our body.

 

     The final stage in the sleep cycle is rapid eye movement sleep, REM. We often experience three to five REM periods in total sleep time. In this stage, our breath becomes quicker than previous stages, our eyes move rapidly, the brain is active and we dream. In addition, if we wake before completing the REM period, a person can experience a period of sleep inertia, that will experience the feeling of drowsiness which occurs for several minutes or even several hours.

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     Although we are sleeping, some brain activities should be done in order to protect us from awakeness as well as refresh our mind . Among the four stages of the sleep cycle, which include light sleep, preparing for deep sleep, deep sleep, and REM sleep in the sleep cycle have different distinguishing features in our brain and body activities. We should sleep early for the purpose of arousing sleep cycle in order to refresh our brain and finally give us the energy for daily life.

 

 

 

 

 

 

Reference

Wikipedia: sleep cycle https://en.wikipedia.org/wiki/Sleep_cycle

Stages of Sleep and Sleep Cycles (Updated on October 10, 2019) https://www.tuck.com/stages/