Overview of
sleep Cycle
- Introduction of Normal sleep cycle
- 2 types of sleep
- 4 stages of sleep cycle
- Sleep waves
- Sleep cycle length
- Sleep Cycle length by age and weight
- Sleep disorders
- Effect of Electronic on sleep cycle
- Do sleep cycle monitoring app works?
What is Sleep Cycle? (Introduction)
Soon after a
person sleep, they go through a series of REM and non-REM type of sleep stages
which completes their one sleep cycle. In the night there are multiple cycles of
sleep which is of 90 minutes each.
In humans
the sleep/wake cycle is controlled by light by activating the suprachiasmatic
nucleus. The suprachiasmatic nucleus is a small bundle of neurons located in
the hypothalamus.
Melanopsin
receptors in the retina of the eye respond to the presence or absence of light
by transmitting signals to the suprachiasmatic nucleus via the optic nerve.
Light
induced activation of the suprachiasmatic nucleus prevents the pineal gland
from producing melatonin, a hormone that otherwise signals biological night and
creates the onset of sleepiness in contrast and absence of light results in the
suprachiasmatic stimulating the pineal gland to produce melatonin, which is
released into the blood.
Usually this
occurs around 9:00 pm as a result melatonin levels in the blood rise sharply
and you begin to feel less alert and sleep becomes more inviting. Melatonin
levels in the blood stay elevated for about 12 hours all through the night
before the light of a new day when they fall back to low date home levels by
about 9:00 am.
This is how
sleep cycle works in human and regulates the rhythm of sleep/awake state in
body in a duration of 24 hours.
Types of sleep
When person
fell asleep, he goes through multiple series of slow-wave sleep (NREM) and
Rapid eye movement sleep (REM), alternating with each other.
Slow-wave
Sleep: it is also
known as non-rapid eye movement sleep. it occupies about 75 % of total sleep. this
sleep is also known as deep sleep which is of most restfulness. This sleep is
associated with a decrease in vascular tone and different vegetative function of
body adding to maintain normal Homeostasis.
Dreams are
unlikely to occur during NREM sleep so they are also called as “Dreamless
Sleep” but some may be present sometimes. Those dreams are not remembered as
consolidation of those dreams do not occur in the brain. It is the sleep that is
experienced in the first hour of sleep after a long duration of wakefulness and mostly
theta waves are associated with this type of sleep.
Rapid Eye
Movement Sleep: In it, there is the rapid and continuous movement of eyes even though the person is in
complete state of sleep. It is an active form of sleep associated with vivid dreaming.
REM sleep occurs in episodes during whole sleep duration and covers about 25%
of total sleep duration in adult.
During REM sleep brainwaves mimic the activity of the brain of an awake person. They are very similar, both containing high-frequency beta waves. The rapid eye movement in this sleep is a result of the intense stream and brain activity that occurs during this stage. It is during this stage of sleep that vivid and powerful dreams usually occur and muscle is paralyzed. Scientists believe this may be to help prevent others from injury while trying to act out her dreams.
This stage is also
characterized by an increase of the heart and respiration rates and their
rhythms become irregular. One of the peculiar characteristics of REM stages is that
it typically gets longer and longer as the night goes by and the last REM stage
can last for an hour.
4 Stages of Sleep cycle
Sleep stages
are defined based on the measurement of electrical activity in the brain using an
electroencephalogram, or EEG. An EEG represents fluctuations in brain
electrical activity in voltage as a waveform of variable frequency and
amplitude.
The American
Academy of Sleep Medicine classifies sleep as consisting of 4 stages. The first
two stages involve drowsiness and light sleep. When someone begins to fall
asleep, they enter:
Stage 1: During this stage, an EEG records
low-amplitude waves of mixed but mostly high frequencies. Stage 1 sleep is the
transition from wakefulness to sleep which typically lasts between 10 to 15
minutes. it is a light sleep where you drift in and out of sleep and can be easily
awakened indeed.
If awakened
in this stage, a person will claim they were never actually asleep. In this
stage
- Theta waves appear on the EEG,
- The eyes move slowly,
- Muscle activity slows during this stage,
- Many people experience sudden muscle contractions preceded by a sensation of falling these are known as hypnagogic jerks,
- Breathing also slows down,
- Heartbeat becomes regular in this stage.
Stage 2: When the person enters stage 2
sleep, this is characterized by the presence of phenomena on an EEG known as
sleep spindles and K complexes. Sleep spindles are trains of high-frequency
waves and K complex involves a biphasic wave that stands out from the rest of
the EEG. Stage 3 sleep is also known as slow-wave sleep or deep sleep. Stage 2
is the main body of sleep and lasts 5 to 15 minutes. It is a light sleep during
which
- Memory consolidation occurs,
- Eye movement stops,
- Brain waves become slower with occasional bursts of rapid brainwaves known as sleep spindles,
- K complexes also appear,
- Heart rate slows down,
- Body temperature decreases in preparation for deep sleep.
Stage 3: When a person enters stage 3,
extremely slow brainwaves called delta waves are interspersed with smaller
faster waves. As a result, this deep sleeps often called slow-wave sleep, which
are low-frequency, high amplitude waves and makeup at least 20% of brain
activity. Stage 3 sleep is thought to be especially important to overall
restfulness. It is during this stage that a person may experience
- Sleep walking,
- Night terrors,
- Talking during one's sleep,
- Bedwetting.
- These behaviours are known as parasomnias
Next, the
sleep passes rapidly back through stage 2 and stage 1 before entering the rapid eye
movement or REM sleep.
Stage 4: In stage four, deep sleep continues
as the brain produces delta waves almost exclusively at this point. You will
sleep through most potential sleep disturbances such as noises and move without
showing any reaction and being awoken during slow-wave sleep will result in a
few minutes of disorientation.
Deep sleep
reduces your sleep drive and provides the most restorative sleep of all the sleep
stages. This is why, if you take a short nap during the day, you're still able to
fall asleep at night but if you take a nap long enough to fall into a deep sleep
you have more difficulty falling asleep at night because you reduced your need
for sleep.
Finally,
after these stages on NREM, cycle person passes in REM sleep. In REM sleep, EEG activity resembles what’s seen
in stage 1 or restful waking. During REM sleep, the muscles are completely relaxed
and limp but the eyes are moving rapidly. This is the time of sleep when our
most vivid dreams are likely to occur. After REM sleep, the person will
sometimes awaken briefly but then will move through the sleep stages again, in
order. Most people will repeat this cycle 4-5 times a night, with each cycle
lasting about 90 minutes.
Stages of sleep |
Definition |
Duration |
Sleep Waves |
Characteristics |
Stage 1 |
The transition from awake to sleep. |
10-15 min |
Alpha and Theta |
Slow breathing and heart rate Relaxation of muscles Hypnogogic jerks |
Stage 2 |
Initial light sleep |
5-15 min |
Sleep spindles and K-complex |
Slow breathing rate Fall in body temperature Simple plot dreams |
Stage 3-4 |
Slow-wave sleep/deep sleep |
10-15 min |
Delta |
Dreamless sleep Hard to wake |
REM Sleep |
Rapid eye movement sleep |
15 min May last an hour-long, as sleep
progress |
Beta |
Vivid dreaming Irregular heart rate and breathing
pattern Raise in body temperature Body is paralyzed Increase in blood pressure |
Sleep Waves/Brain Waves in Sleep Cycle
Electrical
recording of brain activity during sleep has shown different electrical
activity of the brain during different stages of the sleep cycle. The intensity and
pattern of brain activity depend upon excitation of the specific part of the brain
during sleep. The undulation in the recorded electrical potential of the brain
during sleep and wakefulness is called Sleep Waves.
The activity
of a single neuron is not enough to be recorded all the way through skull. Hence
these waves are the result of the summated activity of thousands and millions of
neurons firing synchronously.
There are 4
types of brain waves known as Alpha, Beta, Theta and Delta waves associated
with sleep and also especially known as sleep waves.
Alpha Waves: These waves have a frequency of 8-13
cycles/sec with a voltage of about 50 microvolts. These waves rhythmic in nature
and found in all normal person in the state of wakefulness and in quiet, resting
state of cerebration. These waves are recorded by EEG mostly in occipital,
parietal and frontal region for the scalp. These waves cannot be recorded during
deep sleep as they completely disappear.
Beta
Waves: These waves
have frequencies of 14-80 cycles /sec. These waves are mostly recorded in the region of the parietal and frontal lobe of the brain. These waves frequently replace
alpha waves when the attention of the awake person is directed to a specific type of
mental activity. Those asynchronous beta waves are of higher frequencies and
low voltage.
Theta
Waves: These waves
have frequencies of 4-7 cycles/sec. These waves are mostly recorded on parietal
and temporal lobes. These waves are associated with emotion and are found in
condition like frustration and disappointments. These waves are also indicative
of many brain disorders and degenerative brain disease.
Delta
Waves: These are
universal waves as they include all the brain waves with frequencies of about
1-3.5 cycle/sec. These waves can be recorded in a very deep sleep stage in the cortical region of the brain. They have voltage 2-4 times greater than any other
brain waves. Delta waves are independent of activity in the lower region of the brain
hence can be recorded in the cortex of the brain independently.
Sleep wave
transition as a person goes from Awake to sleep
Beta-Alpha-Theta-Delta
How long is Sleep Cycle?
The first
sleep cycle is about 90 minutes long and in an average, it is about 90-120
minutes long. A person completes 4-5 sleep cycle in one night and as sleep
progresses it last longer.
Asleep
cycle refers to the period of time it takes for an individual to progress
through the stages of sleep. As just outlined, one does not go straight from
deep sleep to REM sleep. However rather a sleep cycle progresses through the
stages of non-REM sleep from light to deep sleep then reverses back from deep
to light sleep, ending with time and REM before starting over in light sleep
again. for example, the order looks something like this
- stage 1 light sleep
- stage 2 light sleep
- Stage 3 deep sleep or slow-wave sleep
- stage 4
- stage 3
- stage 2
- REM sleep
After REM sleep the individual returns to stage 2 of light sleep and begins a new cycle as the night progresses. Individuals spend increasingly more time in REM sleep and correspondingly less time in deep sleep.
Sleep Cycle length by age and weight
There is
great impact of age and weight in the length of the sleep cycle. As in a child, the
duration is more in comparison to adults. similarly, a fat person is more likely
to have more duration of sleep than slim/thin person.
Study has
shown that at different age of life body demand different duration of sleep. Such
as
Age (Years) |
Sleep
Duration (hours) |
0-3
month |
14-17 |
4-11
month |
12-15 |
1-2 |
10-14 |
3-5 |
10-13 |
6-13 |
9-11 |
14-17 |
8-10 |
18-25 |
7-9 |
26-64 |
7-9 |
65+ |
7-8 |
Sleep is
vital for baby's growth and development. Newborns will sleep on and off
throughout the day and night, Waking often for feeding. Older babies aged 3 to
6 months might start moving towards a pattern of 2 to 3-day time sleeps up to 2
hours each. They may still wake at least once a night. By 6 to 12 months,
babies may have their longest sleep at night. Though most this age will still
have a daytime nap. Children will move through periods of light and deep
sleeping and it may differ day to day depending on changes to its regular
routine.
Similarly, in fat person usually, they have more sleep duration which is a result of obesity. Their body metabolism process slows down usually after meal time for metabolizing ingested food. Which make them sleepy all the day.
Sleep Disorders
Common Sleep
Disorders Over 40 million Americans are thought to be dealing with some type of
chronic sleep disorder. In addition to those numbers, there are millions who
have to deal with occasional insomnia or disrupted sleep patterns. To date
there are over 70 different types of sleep disorders with the most common
being:
- Insomnia
- Sleep Apnea
- Restless Leg Syndrome
- Narcolepsy
- Sleep paralysis
- REM Sleep Behaviour Disorder
- Exploding Head Syndrome
- Kleine Levin Syndrome
- Sleep Related Sleeping Disorder
- Sexsomnia
- Nocturnal Death Syndrome
Insomnia
It is the
one that most people are familiar with. It is defined as experiencing poor quality
of sleep and it includes not being able to fall asleep or to stay asleep. The
basic definition of insomnia is that a person can't sleep well and there’s a
daytime consequence. Could be the person’s irritable, they're tired, they're
fatigued, they can't think right, so there's a really negative consequence to
that bad night of sleep. Most adults have had a bad night of sleep before.
Fortunately, most of us get right through it and the next night we're back on
track but some people they develop really a chronic problem where they're just not rightly getting a good night of sleep. And so, we really work to try to undo that
for people.
Sleep
Apnea
It is a
disorder that affects your breathing. People with sleep apnea have marked
reduction in their breathing patterns and they may pause breathing altogether.
There are two different types of sleep apnea:
- Central Sleep Apnea - is where the brain does not send signals to the muscles to breath.
- Obstructive Sleep Apnea - is where the brain does send a signal to the muscles to breathe.
What happens
is that the person's airways obstructed and prevents the correct amount of air
flow to pass. It is possible to suffer from both forms of sleep apnea. Many
people with this condition are obese and have to sleep with breathing apparatus
during the night.
Restless
Leg Syndrome
It is a
sleep disorder that makes a person feel uncomfortable sensations in their legs.
The person may also have an uncontrollable desire to move their legs. This is
not a condition where your legs cramp. A person with this sleep disorder
experience strange feelings in their leg such as tingling, pulling, prickly
feeling or pins and needles feeling. It is considered as a sleep disorder because
person finds difficulty in finding the exact comfortable position of the leg during
sleep which leads to sleep disorientation.
Narcolepsy
It is a
disease that affects your central nervous system. This results in you
experiencing daytime sleepiness, known as EDS. People who have narcolepsy often
have loss of muscular tone, hallucinations, and an inability to move or talk. These
symptoms may be present at once or independently and they can be in various
forms of severity determining the stage disorder.
Sleep
paralysis
It is a
terrifying phenomenon where an individual wakes up during REM sleep, to find
that their body is effectively paralyzed. This petrifying encounter can last
from several seconds to several minutes and is often accompanied by panic
attacks and hallucinations. Stress, depression and lack of sleep have all been
linked to sleep paralysis but, as there is no clear cause of the condition,
there is no guaranteed way to prevent it.
REM Sleep
Behaviour Disorder
REM Sleep
Behaviour prevents an individual’s muscles from paralyzing during sleep. This
means that sufferers will act out their dreams. They can talk, kick and even
walk about as though they were awake. In 2008, father-of-two Brian Thomas
learned how devastating this disorder can be. Whilst acting out a dream in
which he believed he was fighting off intruders, Thomas strangled his wife
Christine to death. Due to his history of the condition and numerous character
references, Thomas was acquitted of the murder.
Exploding
Head Syndrome
It is when
individual shear loud imagined noises when they are on the point of falling
asleep or waking up. The noises have been described as sounding similar to
bombs exploding, cymbals crashing or doors slamming. Some sufferers say they
are accompanied by flashes of light or muscle spasms. And the condition is
surprisingly common. A study by the European Sleep Research Society found that a
staggering 18% of people have experienced it at least once. Exploding Head
Syndrome is caused by a sudden burst of neural activity, most probably brought
on by sleep disruption, such as jet lag or temporary insomnia.
Kleine
Levin Syndrome
Also known
as ‘Sleeping Beauty Syndrome’, Kleene-Levin Syndrome mainly affects teenage
boys. Sufferers spend up to 23 hours a day asleep, sometimes for many days or
weeks in a row. When they are awake, they tend to have heightened hunger and
sexual drives. The syndrome occurs over several years, with breaks of a few
months in between episodes. Nobody knows what causes the condition, although
two-thirds of diagnosed patients suffered from viral infections shortly before
their illness began. Whilst there is no definitive cure for Kleine-Levin Syndrome,
its symptoms appear to be reduced by the mood stabilizer lithium.
Sleep
Related Sleeping Disorder
Most common
in middle-aged women, Sleep-Related Eating Disorder generates uncontrollable
cravings that make sufferers binge on food during the night time. This is not
like conventional mid-night snacking, however, as those affected have no
control over their habits and often don’t remember even leaving their beds.
Whilst sugary snacks and junk foods are the most popular items of choice, some
individuals opt for peculiar concoctions. Sufferers have been known to eat cat
food, cigarette butts or salt sandwiches.
Sexsomnia
In 2014,
Mikael Halverson from Sweden had his conviction for the rape of his female
roommate overturned when it emerged that he suffered from a sinister disorder
called sexennial. Saxonians often engage in sexual activities whilst completely
asleep, with no control over what they do or recollection of their actions.
Most commonly, this involves masturbation or fondling but - it some cases - it
can lead to rape. Dr Kingman Stroh, of the Sleep Center at Case Medical Center
in Cleveland said that it is very difficult to fake sexennial, adjudges look at
previous medical history, sleep studies and character witnesses to make an
assessment.
Nocturnal
Death Syndrome
Sudden
Unexpected Nocturnal Death Syndrome can occur to anyone, often with little or
no prior symptoms. Post-mortems reveal that the majority of victims had
previously unknown heart conditions. The syndrome was first noted in the 1970s,
amongst members of the Hmong people from Laos. Doctors noticed that apparently
healthy Hmong men were dying in their sleep with remarkable frequency. The
deaths generated the mythology of ‘datum’ [da-chop], the idea that a jealous
hag-like woman would sit on their chests at night and stop them breathing. It
is now thought that the Hmong people were so convinced by the idea of dab steam
that their overwhelming fear of it triggered their genetic heart defects,
causing their deaths
If you think you may be suffering from any of these sleep disorders then consult with your doctor for further advice.
Effect of Electronic on sleep cycle
The most
disturbing things for sleep that we do is the overuse of screen time which
includes things like TV, mobile phones, iPads, tablets or any kind of
electronic device. These electronic device effect sleep cycle in various way.
Some most common impact are:
- Disturbed sleep cycle routine
- Melatonin Dysregulation
- Altered Sleep Waves
Disturbed
sleep cycle routine
When you
overuse your screen time, so first of all, it delays you from going to bed
because you get so involved in your tablets or iPhones or screen time that you
become addicted, it raises a chemical in the body called dopamine. This is what
keeps you engaged in these devices. So, it's going to delay your time going to
bed which result in distortion in the sleep cycle and relatively a smaller number
of sleep cycle. it keeps our brain stimulated so this stops you from winding
down at night time, which have sever clinical complication.
Melatonin
Dysregulation
Screens
emits a blue light. Now blue lights mimic daytime and the brain thinks it's
daytime. It stops the release of a hormone in our body called melatonin.
Melatonin is our sleep hormone and this is absolutely crucial that you have a
lot of melatonin at nighttime in the body. It's actually at its highest peak at
night time, ready to be released in time to allow you to go asleep and also to
stay asleep during the night time. It is because it helps to regulate our sleep
cycles during the nighttime and our sleep stages.
Altered
Sleep Waves
Device
radiation, it is another factor that should not be neglected. On an average, any
electronic device radiates a sufficient amount of radiation of very low to very
high frequencies that actually interferes with normal brain waves co-called
sleep waves. They keep stimulating reticular system of the body also known as “sleep
switch of the body” which result in distortion in sleep cycle duration and also
cause wakefulness. it can also add to hyperactivity during the daytime.
To ensure
better sleep health, use of those electronic devices should be monitored and
frequent brake should be taken. These breaks help sensory system and neuron to
get relaxed and help the glial cell to remove metabolic waste produced during the use
of these electronic devices. Doctors suggest that at once no device should be
used more than 30-45 minutes and to maintain such intervals short brakes are
mandatory.
Do Sleep App work?
No, sleep app doesn’t work in reality but at least they are
useful to get some rough data about sleep pattern and sleep cycle.
They are
able to provide a rough idea of how much time you spent in each sleep state but
the accuracy is definitely far from perfect. You can't tell when and how much
you snore which is useful. The sound paints a picture of how much you toss and
turn and rustle in your sheets which provide data that sleep app show.
Those sleep
app working with any kind of physical sleep tracker can be more reliable than
those sleep app that work alone. Mostly trackers work by using a sensor to
monitor movement. An accelerometer is used to measure how fast you move in your
sleep, to help determine how a restful you are. The sleep cycle app, in particular, uses your smartphone’s microphone to monitor sound and help
determine sleep states and movement which do not provide any significant data
to relay on.
In 2016,
study showed that those who tracked sleep on their wearable devices started
sleeping more hours each night. We could make the assumption that this would
also apply to those who use a sleep app.
Though there
are things to be considered with these sleep app, for instance as pet jumping
on your bed can mess with your data and also they do not measure your heart
rate or body temperature like some wearables do which take real-time data
during sleep rather than just working on app-based software.
Both
wearables and sleep apps do not use EEG technology to measure brainwave
patterns like sleep researchers do. Which is one of the most reliable ways to
measure which stage of sleep you're in. According to Dr Basal, there's no way
of wearables or sleep apps to measure your REM sleep, the smart wakeup
functions or sleep apps are meant to wake you up during light states of sleep
so you don't feel groggy in the morning.
if you're serious about tracking your sleep
with higher accuracy then it is better to use something like a wearables, like
Fitness Band or fitness Ring.
Because it measures your hot dynamics pulse strength, body temperature and many more parameter based on the hardware, you get more reliable data than just putting a phone next to your bed and basically crossing your fingers and hoping for the best before you go to sleep.