There was a time when people used to compare sleep to death. They thought that a human body stops working, both physically and mentally while sleeping. But the truth is far from that fact! Studies over the last half a decade or so have proven that there are a lot of activities going on in our body, like eye movements or brain responses even when we are asleep. According to the experts, the sleeping process is the repetition of a cycle called the Sleep cycle. In this article, we will shed some light on this topic.
What Is The Sleep Cycle?
During sleeping, the physical and mental responses of the human body changes in a progressive manner. They do not just go on/off instantly. These changes are divided into five stages, the combination of which is called a sleep cycle. During sleeping, the sleep cycle repeats itself multiple times. While some stages of the cycle are very light, some others are quite deep that the person can not be awakened easily. The length of each cycle is around 90-110 minutes. But their duration changes as the sleep progresses. An average adult human being needs 7-8 hours of daily sleep to stay fit. Those 7-8 hours of sleep consists of 4-5 sleep cycles, out of which, the middle ones are usually the longest.
The Stages Of A Sleep Cycle
There are five stages in the sleep cycle of an adult person- stage 1, 2, 3, 4 and REM (Rapid Eye Movement) stage. The first four stages are collectively named as NREM (Non-Rapid Eye Movement) stage. But some experts tend to combine the 3rd and the 4th stages to make a single one. Several physical factors, such as eye movement, ease of arousal, muscle activity or brain activity, differentiates these five stages of sleep.
A person is barely asleep in this drowsy stage of the cycle. So, if the person wakes up during this stage, then he can even claim to be not falling asleep. The physical and the mental changes in this stage include decreasing eye movement and muscle activity, a sensation of falling, etc.
The second stage of the sleep cycle is also a light one, although the physical and mental responses of the body further diminish. If you are trying to have a “power nap,” then this is the targeted stage for you. In this preparatory stage of a deep sleep, the eye movement stops, body temperature and blood pressure decrease considerably.
Stage 3 And 4:
These are the period of deep sleep in the cycle. In this stage, the brain emits languid brain waves called delta waves. These waves have slow speed and high amplitude. The 3rd and 4th stages are also named as the “Restorative stages” of the sleep cycle. It is in these stages that the muscles and tissues start to repair from the day’s fatigue and restores the energy to work on the following day. The Parasomnia sleeping disorder is also the characteristic of these stages.
Irregular and fast breathing and rapid eye movement characterize this final stage of sleep. According to the NSF, in the REM stage, “the brain is active, and the body is paralyzed”. During REM, our brain processes the daily information so that they stay in our memory for long. This data processing also results in dreams during sleeping. As the sleep progresses, the percentage of the REM period in a sleep cycle increases. That is why we dream more in the early morning.
The pattern of the sleep cycle, their length and natural timing changes as a person ages. A newborn baby does not have the five aforementioned distinctive stages of a sleep cycle; they fully develop during the toddler years only. Similarly, an older person spends more time in the lighter stages than the deep sleep stages as compared to a teenager. Scientists have been able to explain some of these changes, while some others remain unsolved. But as time goes by, we understand our sleep better than before.