Sleep is a state when our senses and motor activity are relatively suspended; there is total or partial unconsciousness, and all voluntary muscles are inactive. Sleep is more reversible than hibernation or coma, but responds less to stimuli than quiet wakefulness. Sleep is the body's rest cycle.
This Medical News Today article provides the essential details about sleep, including how much sleep we need, what a sleep debt is, sleep deprivation, and sleep disorders.
At the end of some sections we have included updates from MNT's news stories.
Sleep is a heightened anabolic state - a period when our bodies are producing new bone, muscular and nervous tissue; a period when growth and repairs occur.
Most animals sleep, including mammals (humans are mammals), birds, a significant number of reptiles, amphibians, and fish.
A complex group of hormones trigger sleep. These hormones respond to cues within our body, as well as in the environment. Approximately 80% of sleep time is without dreams, this period of mainly dreamless sleep is known as NREM (non-rapid eye movement). Dreams occur mainly during REM (rapid eye movement).
According to the National Institutes of Health1, a number of crucial tasks are carried out by the human body during sleep to help maintain good health so that we can function at our best. Not getting enough sleep can be dangerous for both our physical and mental health.
Many people find it hard to fall or stay asleep. The Sleep Disorders Center2 at the University of Maryland informs that approximately 9-12% of the U.S. population have chronic insomnia.
NREM (non-rapid eye movement) sleep - during this period our heart and breathing rates are slow, and blood pressure drops. The person does not move about much.
NREM sleep is divided into three or four stages:
Stage 1 sleep - the transition period between wakefulness and sleep. There is slow eye movement. Alpha waves make way for Theta waves. If someone in this stage is woken up, they think they have not been asleep. Hypnic jerks (involuntary twitches) commonly occur during this stage.
Stage 2 sleep - 50% of our sleeping time is in Level 2. The heart and breathing rates slow right down. The eyes do not move at all. People hardly ever dream during this stage. Even though the sleeper is quiet, they can be easily awakened.
Stages 3 & 4 sleep - used to be divided into 3 and 4, but is now more commonly grouped into just Stage 3. Stage 3 used to be the transition period between 2 and 4, when delta waves started to occur. Delta waves are associated with deep sleep, and dominate Stage 4 sleep. There is some dreaming in this stage, more than in stages 1 and 2, but much less than in REM sleep.
REM (rapid eye movement) sleep - a normal stage of sleep that makes up between 20% and 25% of total sleep time. There is rapid movement of the eyes and low muscle tone.
Babies spend much more of a night's sleep in REM than older people.
Humans generally experience four or five periods of REM sleep during a typical full sleeping session; the last one is longer than the first.
Some people may have a brief period of light sleep, during which they are easily awakened, shortly after an REM session.
Sleep experts say our brain neurons are about as active during REM as they are when we are awake. However, atonia paralyzes the body during REM. Atonia is an extremely relaxed state of skeletal muscles.
If we remember a dream, it would have occurred during REM.
How much sleep do I need?
Our sleep requirements vary according to our age, lifestyle, when sleep occurs, how fixed our routines are, our general state of health, and our individual circadian rhythms (body clock). The figures below are general approximations, depending on age:
Daily sleep requirement, according to age and condition:
Newborn baby - up to 18 hours
1 to 12 months of age - 14 to 18 hours
1 to 3 years of age - 12 to 15 hours. A study found that midday naps boost learning in preschoolers.
3 to 5 years of age - 11 to 13 hours
5 to 12 years of age - 9 to 11 hours
Teenagers - 9 to 10 hours
Adults - 7 to 8+ hours
Women during pregnancy - at least 8 hours
It is important to remember that sleep requirements vary between individuals of the same age, health and lifestyle - sleep needs are individual. The figures above should at best be seen as a rough guide. A 28 year-old man may function well with 7 hours sleep each day, while a work colleague of the same age, health, height, weight and lifestyle may need 8 hours.
Source : MNT
Our sleep requirements vary according to our age, lifestyle, when sleep occurs, how fixed our routines are, our general state of health, and our individual circadian rhythms (body clock). The figures below are general approximations, depending on age:
Daily sleep requirement, according to age and condition:
Newborn baby - up to 18 hours
1 to 12 months of age - 14 to 18 hours
1 to 3 years of age - 12 to 15 hours. A study found that midday naps boost learning in preschoolers.
3 to 5 years of age - 11 to 13 hours
5 to 12 years of age - 9 to 11 hours
Teenagers - 9 to 10 hours
Adults - 7 to 8+ hours
Women during pregnancy - at least 8 hours
It is important to remember that sleep requirements vary between individuals of the same age, health and lifestyle - sleep needs are individual. The figures above should at best be seen as a rough guide. A 28 year-old man may function well with 7 hours sleep each day, while a work colleague of the same age, health, height, weight and lifestyle may need 8 hours.
Source : MNT
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