Before we go deep down to understand the Sleep, let’s discuss Biological rhythm. So, the biological rhythm varies from a fraction of second to the monthly order. The heartbeat has the shorter span of biological rhythm, whereas women’s menstruation cycle had the monthly biological rhythm. Some of the biological rhythms occur on daily basis like rising and fall of blood pressure, changes in body temperature and chemicals, etc. Among these daily biological rhythms, the one is the Sleep-Wake Cycle; hence, we could conclude that it is one of the parts of Biological rhythm.
It is 24 hours rhythm which takes about a day to complete the cycle. This is actually the Sleep-wake cycle. This Circadian cycle is basically controlled by the small part of the brain which is inside the hypothalamus. A highly sensitive to light nucleus called as Suprachiasmatic nucleus which is inside the hypothalamus tell people when to wake up and when to fall asleep. It sends commands to the pineal gland to release melatonin. Melatonin is the hormone which is responsible to make people fall asleep.
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Why do We Sleep?
Sleep is one of the activities of our life cycle. Some people are short sleepers, they need only 4 or 5 hours of the nap, whereas, others are long sleepers and they require 9 hours of the nap or more than that.
The amount of sleep we get that can have an impact on our health. As we age, we seem to sleep less at night until the average sleeping hours reaches 6 hours.
Some people have microsleeps. It sometimes happens while driving the car, listening lecture, while working, etc. The microsleeps may cause danger to the life. Microsleep occurs only for a few seconds.
The real purpose of sleep is well explained by its theories. Theory of sleep gives the real answer to why we sleep!
- The Adaptive Theory of Sleep: Sleep, which is a product of evolution. The adaptive theory explains that animals and humans developed different sleep patterns. These sleep patterns are developed to avoid own presence when their predators are most active during their normal hunting hours, which typically would be at night.
- The Restorative Theory of Sleep: This theory is directly related to the biological changes within our body. According to the restorative theory of sleep, the sleep is necessary for the physical well-being or health of the body. As per this theory, sleep helps to replenish the chemicals that were used up during the day’s activities. Some other chemicals that were secreted in excess which become toxic, if remain kept in the body, those chemicals are removed during sleep. Some of the important benefits of sleep are as follows:
- Sleep enhances brain plasticity
- Most bodily growth and repair occur at deepest sleep
- Sleep forms memories
From the above theories, we may conclude that Adaptive theory explains why people sleep when they do, whereas, the Restorative theory explains why people need to sleep.
It is simply defined as the significant loss of sleep which causes losses in concentration while doing normal activities, thus, resulting in irritability. Some of the problems generated due to sleep deprivations are listed below:
- Unable to perform the more complex task
- Loss of memory
- Improper physical functioning
- Loss of concentration
- Delay in the onset of puberty
- Increased risk of insulin (Diabetic problems)
- Weight gain
Some of the typical symptoms of sleep deprivation include-
- Trembling hands
- Staring off
- Droopy eyelids
Types of Sleep
There are two kinds of sleep, which includes-
- Rapid eye movement sleep (REM): A stage of sleep in which most of the person’s dreaming takes place. In REM, voluntary muscles stop, hence, a person moves very little during sleep; additionally, the person’s eyes move rapidly inside the eyelids this happens due to dreaming.
- Non-rapid eye movement sleep (NREM): It is more restful kind of sleep in which a person goes from a lighter stage of sleep to the deeper stage. In NREM, person’s voluntary actions are active, thus, a person is free to move their body which results in kicking.
Different Stages of the Sleep
This is a machine which allows scientists to record different stages of sleep and kind of sleep a person is going through in graphical pattern. The graphical patterns are designated as different waves, which are discussed below:
- Beta Waves: When a person is involved in the mental activity and widely awake, then the waves shown on EEG will be the Beta waves. These waves are very small and very fast.
- Alpha Waves: When a person becomes a little drowsy and gradually relaxes and achieve light sleep mode then the generated wave pattern is alpha waves. These waves are slightly larger and slower.
- Theta Waves: When, further, a person achieves early stages of sleep then alpha waves is replaced by theta waves, which is even slower and larger than the Alpha waves.
- Delta Waves: When a person achieves the deepest stage of sleep then the longest and slower waves patterns are called Delta waves.
Above graph represents the sleep stages of a person. Let’s discuss different stages in detail for better understanding of the graph.
Stage 2 (N1): Light Sleep
When theta waves activity increases and alpha waves activity go away then the person is said to be entering in light sleep mode, which is designated as N1 in above graphical representation. If people are awakened in this stage, then it is hard for them to believe that they are in the state of sleep. They may experience vivid visual events in the form of Hallucinations.
Stage 3 (N2): Sleep Spindles
Sleep spindles occur when people drift further into the sleep which is basically caused by the drop in body temperature. At this stage, theta waves still predominate, but people will be aware that they are asleep when they are awakened. In this stage, heart rate slows, shallow and irregular breathing occurs.
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Stage 4 (N3): Delta Waves
This stage welcomes the slowest and largest waves of the sleepy night. Brain activities increase from 20% to more than 50% due to theta waves. A person achieves the deepest level of sleep at this stage which is technically called as Slow wave sleep. Major bodily progression occurs at this stage. Pituitary glands release growth hormones which reach its peak level.
It’s very hard that people are awake at this stage. If they are awake, then they feel disoriented and confused at earliest.
Stage 1 (R): Rapid Eye Movement
After spending some time in at N3 level, the sleeping person starts going back to N2, then N1 and finally he reaches at stage 1 where his body temperature increases to nearly waking level, eye movements starts under the eyelids, heart beats faster and the brain starts resembling the beta waves. The person is still sleeping but he is in the Rapid eye movement stage.
When he is awakened in this stage then he is being reported in a dream state. People see 90% of the dream at this stage only. People do see dreams in NERM state but there are quite variations in dreams happening in these two states.
When a person is dreaming in REM state, the dreams tend to be more vivid, detailed, longer and bizarre dream as compared to the NREM state. NREM state has a shorter span of dreaming which is mainly related to thoughts of the daily occurrences.
Sleep paralysis occurs when a person is unable to move their body muscles under normal circumstances in REM dream. Voluntary muscles get paralyzed in this stage.
Sleep purpose with respect to REM & NREM sleep
Both REM and NREM, sleep tends to fulfill different purposes.
When a person spends the entire day in doing lots of physical activity and drained with all sorts of energies then he would spend more time in NREM deep sleep, whereas, when a person leads emotionally stressful day then he would release all the day’s stresses and tensions in REM sleep. Hence, both types of sleep solve different purposes of human life.
REM Rebound: This phenomenon occurs when a person is deprived of REM sleep, so he adds up an additional hour in taking REM sleep the next day.