Sleep: Stages and characteristics
The sleep is need for all human beings and most of other animals, because sleep is
seclusion. Although we have a fondness for foods and sex, we give time for sleeping than them.
Sleep is the primary function of the brain and plays an essential role in an individual’s
performance, learning ability and physical movement. When there is no enough sleeping that
brought by internal procedure in automatically. On average we spend about 30% of our live
asleep. In number, most of us will sleep for over 175,000 hours is our lifetime. It’s common for
human being, beast and also trees. Some of the sleeping trees can be seen in environment. Even
lifeless machines need this seclusion.
When researcher study on sleep, relies on three fundamental measures, first one is gross
brain wave activity measures by an electroencephalogram (EEG). This machine detects
abnormalities in our brain waves or electrical activity of our brain. The EEG represents the sum
of the post synaptic potentials of a large number of neurons within some portion of the cerebral
cortex. With the help of electromyogram (EMG) machine measuring of muscle tone is second.
Third one is electro-oculogram (EOG) which is recorded eye movements. EEG is most important
for measure in differentiating between the stages and EMG and EOG are useful in measure
difference of rapid eye movement.
In sleep, the eyes are closed and several nervous system centers are inactive. There are
two main stages of sleep that alternate at about 90-minute intervals. They’re
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Rapid Eye Movement Sleep ( REM)
Non-Rapid Eye Movement (MREM/Non-REM)
In the rapid eye movement sleep the eyes move rapidly in various direction. People enter
REM sleep after 90 minutes of sleep. During this stage brain is almost active and the body is
paralyzed. Breathing can become fast and irregular and dreams can be seen in this stage.
In non-rapid eye movement sleep, the brain is less active but the body can move. NonREM sleep is composed of four stages that are differentiated on the basis of EEG characteristics.
When normal individuals first fall asleep, they enter Stage 1 and then progress through Stages 2,
3, and 4 of NREM sleep. Stages 3 and 4 are often called slow wave sleep or delta sleep because
they are characterized by high amplitude, slow waves (delta waves) on EEG.
It’s clear that the brain moves through five different stages. In here I discuss those stages and
characteristics.
Rapid Eye Movement Sleep ( REM)
Rapid eye movement sleep, in short for REM is basic stage of sleep. Fast eye movement
sleep, also known as REM sleep, is the third stage of your sleep cycle. It is characterized by
small, variable-rapid brain waves, rapid eye movements, heart rate, and muscle paralysis. When
your body first enters this stage, it will stay in REM sleep for 90 to 110 minutes. Your time at
this stage will increase throughout the night.
When we enter REM sleep, brain activity increases again, meaning sleep is not as deep. The
activity levels are like when you’re awake. That’s why REM sleep is the stage where we’ll have
intense dreams. At the same time, major muscles that you normally control such as arms and legs
can’t move. In effect, they become temporarily paralyzed. Usually, REM sleep arrives about an
hour and a half after you go to sleep. The first REM period lasts about 10 minutes. Each REM
stage that follows gets longer and longer. During REM sleep, the body and brain go through
several changes, including:
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Rapid movement of the eyes
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Fast and irregular breathing
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Increased heart rate (to near waking levels)
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Changes in body temperature
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Increased blood pressure
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Brain activity similar to that seen while awake
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Increased oxygen consumption by the brain
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Sexual arousal in both men and women
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Twitching of the face and limbs
In most people, a state of temporary paralysis is experienced as the brain signals the spinal
cord to cease movement of the arms and legs. This lack of muscle activity is known as atonia,
and it may be a protective mechanism to prevent injury that might be caused by acting out our
dreams.
REM sleep is often associated with very vivid dreams due to the increase in brain activity.
Because the muscles are immobilized yet the brain is very active, this stage of sleep is sometimes
Non-Rapid Eye Movement (MREM/NonREM)
NREM sleep is divided into three separate sub-stages: N1, N2 and N3 or slow-wave sleep. Each
of these stages can last from 5 to 15 minutes or more and NREM stages may repeat until REM
sleep is attained.
Stage 1:
Stage one of sleep, also known as the transitional phase, occurs when one finds themselves
floating in and out of consciousness. During this NREM stage, you may be partially awake while
your mind begins to drift off. This stage lasts about 5 to 10 minutes and is the transition period
between wakefulness and sleep and can also occur during transitions between periods of deep
sleep and REM as well. The muscles in the body remain active and a person in this stage of
NREM sleep can be easily awoken. Some points are following:
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Everything starts to slow down, including your eye movement and muscle activity.
Your eyes stay closed. If you get woken from stage 1 sleep, you may feel as if you
haven’t slept at all. You may remember pieces of images.
Sometimes, you may feel like you’re starting to fall and then experience a sudden muscle
contraction. Healthcare providers call this motion hypnic myoclonic or hypnic jerk.
Hypnic jerks are common and not anything to be concerned about as this occurrence is
unlikely to cause any complications or side effects.
Stage 2:
This stage is a period of light sleep with slowing brain waves and muscle relaxation. It is
generally the period between drowsiness and light sleep and deep slow wave sleep. Adults spend
about 50% of their entire night’s sleep in stage 2 sleep. Toward the end of a period of stage 2
sleep, as the body prepares to enter deep sleep, the heart rate slows and body temperature
decreases. During stage two, eye movement stops and brain waves slow with the occasional burst
of waves called sleep spindles. Stage two can also be characterized by the unstructured periods
that alternate between muscle tone and muscle relaxation.
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This period of light sleep features periods of muscle tone (muscles partially contracting)
mixed with periods of muscle relaxation.
Your eye movement stops, heart rate slows and body temperature decreases.
Brain waves become slower. Occasionally, you’ll have a burst of rapid waves called
sleep spindles.
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Your body prepares to enter deep sleep.
Stages 3
Stage N3, slow-wave sleep, assists the body to repair and regenerate tissues. A recent study
suggests this is also the stage during which the brain flushes out toxic waste. According to a
study from Boston University, research shows cerebrospinal fluid may clean out toxic waste
from the brain, and that slow- wave sleep greatly aids in the process. This stage of sleep may last
up to 40 minutes.
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This stage is deep sleep.
During this stage, your brain produces delta waves, very slow brain waves.
It’s hard for someone to wake you up during this stage.
You have no eye movement or muscle activity.
If you’re woken up, you may feel groggy and disoriented for a few minutes.
Comparison of stages of sleep
Category
Waking
Non-REM sleep
REM sleep
EEG characteristics
Low voltage, fast
High voltage, slow
(EEG
synchronization)
Low voltage, fast
Eye movements
Normal tracking
Absent
Muscle tone (EMG)
Present
Variable; generally
reduced
Specific pattern of
rapid eye movements
Absent (except ocular
muscles)