Sleep Cycle And The Stages Of Sleep 

What is sleep?
Sleep is a natural and temporary state of rest for all living beings. During sleep, the living beings become physically inactive and unaware of the surrounding environment. 

Sleep is a crucial aspect of physical, mental, and emotional well-being. Good quality sleep helps you refresh and rejuvenate by repairing and recharging your body. The stages of sleep and sleep cycles play a crucial role in this process. Sleep heals and re-energizes you when you are tired, sick, or stressed.

This article helps you understand sleep through the different sleep stages and cycles.

What are sleep stages?
When you sleep, your brain passes through five different stages of sleep, ranging from light to deep sleep. At night your body goes through the five stages four to five times. REM (rapid eye movement) and NREM (non-rapid eye movement) are the two categories of sleep stages.

Every stage of sleep plays a crucial role in the sleep cycle and has its own function to rejuvenate and recharge your body for the next day. The sleep stages help balance hormones, muscle recovery, and memory formation.

Sleep cycle stage 1:
The first stage is called the transitional phase, and it only takes a few seconds to fall asleep. It is a non-REM stage, which means you have not entered deep sleep. You hear everything going on around you. Even the slightest sound wakes you up. In this sleep stage, you might experience occasional muscle jerks, known as hypnic myoclonia, sleep twitch, or hypnic jerk. These jerks are a result of involuntary muscular contractions.  

Sleep cycle stage 2:
The second sleep stage is also a non-REM stage, but your sleep is stronger than the first stage. It is the longest stage in your sleep cycle. In this phase, your muscles relax, your heartbeat slows down, core body temperature drops, eye movements stop, and you completely drift off to sleep. Although this is a light sleep stage, you spend more than 50 percent of your sleep in this phase.

Sleep cycle stage 3:
This stage is the most crucial phase of your sleep cycle. It lasts between 10 to 40 minutes, and your sleep is the deepest. Your heart rate and breathing are at the lowest in this phase. You have no consciousness of what is happening around you. The growth and restoration hormones release during this phase.

Sleep cycle stage 4:
The fourth stage is also a non-REM phase, but the sleep resembles being in a coma because the heart rate and the body temperature are at their lowest. Your breathing becomes rhythmic, and there are no muscle movements. This stage lasts around 30 minutes, and your brain produces the delta. The delta waves are associated with relaxation and sleep and enhance your body’s healing abilities. 

Sleep cycle stage 5:
The final and the only REM phase in the sleep cycle. In this stage, your brain begins to get active. In the previous four stages both your mind and body are at rest, healing and recharging. But in the REM stage, your mind starts waking up and getting active while your body is still inactive. 

Your breathing is shallow and irregular, while your heart rate and blood pressure rise. 

Factors affecting sleep stages and sleep cycles

The sleep cycle comprises these five stages. But the sleep cycle is not the same in every person. 

The following external factors are responsible for regulating the sleep cycle: 

  • Age
  • Circadian rhythm
  • The previous period of wakefulness
  • Ambient temperature
  • Environmental factors
  • Stress
  • Medications
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