Sleep: Sleep Stages, REM Sleep, Biological, and Circadian Rhythms

Sleep is an essential process of life. It is as important to our well-being as the water we drink, the air we breathe, and the food we eat. Today busy people most of the time regard sleep as a waste of time. Peoples take time away from sleep to tend to affairs of the day.  Today sleep deprivation is a common feature of our society. Sleep is affecting children and adults alike. 

          Sleep is an essential human health element. It is supporting a wide range of systems including immune function, emotional regulation, cognition, and metabolism. To understand everything that sleep does, however, it is necessary to understand what sleep is.

Sleep: Sleep Stages, REM Sleep, Biological, and Circadian Rhythms


           People spend one-third of our lives sleeping. Given the average life expectancy falls between 75 and 80 years old. People can expect to spend approximately 25 years of our lives sleeping. Every animal spends different time for sleeping in his life so some animals can go extended periods of time without sleep and without apparent negative consequences (e.g., dolphins); other animals never sleep (e.g., several fish and amphibian species); yet some animals (e.g., rats) die after two weeks of sleep deprivation.


Sleep is a state of unconsciousness in which the mind and brain apparently turn off the functions that create an experience. During sleep, we become less aware of our surroundings. Sleep also inhibited sensory activity and inhibition of nearly all voluntary muscles during REM ( rapid eye movement ) and reduced muscle activity.

             Sleep is very different from disorders of consciousness, states of coma, and death by the fact. sleep is an active period in which a lot of important processing, restoration, improve health, and  pieces of information are transferred from more tentative, STM(short-term memory) to stronger, LTM(long-term memory) a process called “consolidation.” 

Biological Rhythms and Circadian Rhythms

We may go for a while without sleep and sometimes, we can try to stay awake, but eventually, we must sleep. Many reasons for this fact is but sleep is one of the biological rhythms of the human body, natural cycles of activity that the body must go through.

          Some biological rhythms are far shorter and some longer. e.g. the cycle of a woman’s menstruation, the beat of the heart. But many biological rhythms are daily bases, like the rise and fall of blood pressure and body temperature.


The sleep-wake cycle is a circadian rhythm. The circadian comes from two Latin words, circa meaning-“about” and diem meaning-“day”. So a circadian rhythm is a naturally occurring 24- hour cycle that takes “about a day” to complete. The sleep-wake cycle is ultimately controlled by the hypothalamus, the tiny section of the brain.

        Human beings tend to have a rest-activity cycle of about 25.1 hours. The explanation of a slight deviation from 24 hours is very difficult. but many people have to want to stay up a little later each night and wake up a little later each day under this tendency. We’re 25.1-hour people living in a 24-hour world.


Wake: When a person is awake, EEG patterns exhibit two types of waves: Beta and Alpha.

Beta waves: 

Beta waves reflect concentration and alertness. These waves are the lowest in amplitude and highest in frequency.

Alpha waves

When we are relaxed but still awake, our brain waves slow down, increase in amplitude, and low in frequency. These waves, associated with relaxation or drowsiness, are called alpha waves

The electroencephalogram (EEG): Brain waves.

The electrooculogram (EOG): Eye movement. 

The electromyogram (EMG) :. Muscle tension.

Stages of sleep

Sleep is divided into two major phases: Non-REM (NREM) sleep and REM sleep. 

Rapid eye movement (REM) sleep – movements of the eyes under closed eyelids and dreaming 

– Brain waves during wakefulness appear very similar to brain waves during REM sleep.

Non-REM sleep (NREM): NREM has relatively few eye movements and little dreaming; those that occur are slow. Non-REM (NREM) sleep is subdivided into four stages distinguished from each other and each marked by unique brain wave patterns.

First Stage N1 (Non-REM1) Sleep: When we are just falling asleep, we enter the first stage of non-REM sleep.  Stage N1 is characterized by drowsy sleep. People enter light sleep (Stage 1 sleep) or drowsy sleep, slow heart rate, and relax body muscles.

           In this light stage of sleep, which lasts for 5 to 10 minutes,  50 percent brain activity powers down, producing theta waves, which brain waves occur three to seven times per second. These waves are slower than the alpha waves of eight to 12 times per second when we’re quiet and relaxed.

      Brain waves are slower and lower energy waves, slower in frequency, and greater in amplitude than alpha waves.

Second Stage N2 (Non-REM2) Sleep: After about 5–7 minutes in N1, we move to N2 sleep. In stage N2 sleep, muscle activity decreases, our brain waves slow down, even more, body temperature drops further and the body goes into a state of deep relaxation. We are no longer consciously aware of the environment. 

Two major electrical phenomena: k-complexes and sleep spindles.

Sleep Spindles: Theta waves still dominate the activity of the brain, but they are interrupted by brief bursts of activity known as sleep spindles (electrical activity 12–14 cycles a second).

Asleep spindle involves a sudden increase in high-frequency wave bursts that may be important for learning and memory. Sleep spindles (It) may help prevent the sleeping brain from being aroused by external stimuli, that is a true boundary of sleep.

K-Complexes: The K-complexes appearance is often associated with stage 2 sleep and also appears only when we’re asleep. As our brain activity decelerates, our muscles relax, even more, our eye movements cease,  our heart rate slows, and our body temperature decreases. The amplitude pattern of brain activity is high in K-complex that may help cases occur in response to environmental stimuli.

Third Stage N3 and Fourth Stage N4 

Stage N3 (Non-REM3) Sleep:

After about 10 to 30 minutes, light sleep gives way to much deeper slow-wave, called delta waves, the slowest and highest amplitude brain waves during sleep, which is as slow as one to two cycles a second and a further loss of consciousness.

Stage N4 (Non-REM4) Sleep:

we pass through stage 3 and then enter into stage 4 sleep.3 and 4  stages are often referred to as delta sleep (delta waves). If you want to feel fully rested in the morning, you need to experience these deeper stages of sleep throughout the night.  People believe in a common myth is that drinking alcohol is a good way to come (catch up on) sleep. Not quite. people use drinking alcohol in the night, they feel more tired the next day because alcohol suppresses delta sleep. In stage 4 If people make a loud noise, the sleeper will wake up in a state of confusion and may not remember the noise.

What is REM Sleep?

Depending on his or her age, a sleeper typically spends about 20 to 30 minutes in

slow-wave sleep. After that, the subject is dreaming and has entered another stage of sleep, called rapid eye movement (REM) sleep.

           REM sleep is a relatively deep stage of sleep marked by rapid eye movements,low-amplitude brain waves, and high-frequency activity. His heart rate and respiration rate quicken, almost as if he were awake and exercising. The person showing that the brain is active, supported by increases in oxygen consumption, blood flow, and neural firing in many brain structures. In this stage voluntary muscles are no movement during REM sleep in a normal individual; REM sleep is often referred to as paradoxical sleep because the brain may be very active, the body (muscles) isn’t. 

           As the night goes on, the Non-REM total cycle remains at approximately  90 to 100 minutes, a second REM period (ensues) arises, and this pattern of alternating non-REM and REM sleep periods continue throughout the night. 

READ MORE ARTICLE: Psychology: Definition, Types, History, Schools, Importance

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