What Is Sleep? How Much Sleep Do I Need?

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Main Category: Sleep / Sleep Disorders / Insomnia
Article Date: 26 Jul 2010 - 8:00 PDT

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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.

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 Medilexicon's medical dictionary:

Sleep is A physiologic state of relative unconsciousness and inaction of the voluntary muscles, the need for which recurs periodically. The stages of sleep have been variously defined in terms of depth (light, deep), EEG characteristics (delta waves, synchronization), physiologic characteristics (REM, NREM), and presumed anatomic level (pontine, mesencephalic, rhombencephalic, rolandic, etc.).

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
• 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.

What is sleep debt?

Sleep debt is the cumulative result of not getting enough sleep. Sleep debt can be caused by partial or total sleep deprivation. Partial sleep deprivation builds up if you spend too many days or weeks getting less sleep each day than you need. Total sleep deprivation refers to spending whole days without getting any sleep at all.

A large sleep debt can lead to physical and mental fatigue, and eventually, physical and mental health problems.

As your sleep debt increases, your ability to perform high-level cognitive functions goes down.

What is sleep deprivation?

This is a sleep disorder - the individual has too little sleep. Laboratory animals with long-term sleep deprivation eventually die.

Sleep deprivation affects millions of people globally. According to the NIH (National Institutes of Health), USA, about 50 to 70 million people in the USA are thought to be affected by sleep deprivation or other sleep related disorders.

Sleep deprivation (lack of sleep) can eventually lead to:

• Physical inactivity (link to article)
• Increased urine production and more salt in urine. Especially in males. (Link to article)
• Body aches and pains, especially in the muscles
• Nausea
• Dizziness
• Slower healing process
• Dry mouth
• Hallucinations
• Hand tremors
• Headaches
• Chronic migraine (link to article)
• Hypertension (high blood pressure)
• Higher risk of developing diabetes
• Higher risk of developing fibromyalgia
• Irritability, moodiness, anxiety. Tantrums in children.
• Memory problems
• Obesity (link to article)
• Problems concentrating
• Problems with attention span
• Accidents when driving or operating heavy machinery (link to article)
• Problems with decision-making (link to article)
• Problems with information processing (link to article)
• Heart disease (link to article)

What is a sleep disorder (somnipathy)?

Somnipathy is any disorder that affects, undermines, disrupts, or involves sleep. Although not medically significant, snoring is probably the most common sleep disorder. Some sleep disorders may seriously affect the individuals mental, emotional and physical health.

Examples of sleep disorders:

• Bruxism - the patient grinds or clenches his/her teeth during sleep.
• Cataplexy - often affects people with narcolepsy. The individual suddenly feels extremely weak and collapses during moments of strong emotion, such as anger, surprise, laughter or fear.
• DSPS (delayed sleep phase syndrome) - a disorder of circadian rhythms. The person cannot fall asleep or wake up at normally accepted times.
• Hypopnea syndrome - breathing is either too shallow or slow during sleep.
• Narcolepsy - a chronic sleep disorder where the brain is unable to regulate the body's sleep-wake cycles. People with narcolepsy may feel an overwhelming urge to sleep at various points in the day, and they will often fall asleep spontaneously for a few seconds to a few minutes. In extreme cases, people with narcolepsy will remain asleep for over an hour.
• Nocturia - the individual has to keep getting up at night to urinate.
• Obstructive sleep apnea - a sleep disorder in which the patient stops breathing for 10 seconds or more during sleep. It is caused by relaxation of the throat muscles; the soft tissue in the rear of the throat collapses and closes, resulting in blocked airways. There is a lack of deep sleep.
• Pavor nocturnus - also known as night terror. The individual wakes up from sleep with terror. Episodes of fear, flailing and screaming while asleep. Often linked to sleepwalking.
• PLMD (periodic limb movement disorder) - sudden jerks of an arm or leg during sleep.
• Primary insomnia - the individual finds it hard to either fall asleep or stay asleep, or both. No underlying cause is detected.
• RBD (rapid eye movement behavior disorder) - abnormal behavior during REM (rapid eye movement) phase. Usually, during this phase the muscle are totally still, as if paralyzed (atonia). The atonia is lost during REM sleep, when most dreaming occurs. The body starts to twitch and undergo complex integrated movements - as if the patient were physically acting out the dream. There is a risk of injury to the bed partner.
• RLS (restless legs syndrome) - a disorder which causes a strong urge to move your legs. This urge is frequently accompanied with strange and unpleasant sensations in your legs. Patients say the only way to relieve those unpleasant feelings is to move their legs.
• Somnambulism - sleepwalking
• Somniphobia (hypnophobia) - an abnormal fear of sleep.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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