Sleep

Editor-In-Chief: Prab R Tumpati, MD
Obesity, Sleep & Internal medicine
Founder, WikiMD Wellnesspedia &
W8MD medical weight loss and sleep centers

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List of terms related to Sleep

Sleep is a physiological state of rest seen in most animals, including humans.

What sleep is for

Generally, the reason for sleep is that the brain has work to do during sleep. The details are not fully understood, but it is important to get enough sleep for the body and the brain to be healthy and work properly. Usually animals (and people) sleep at periodic intervals, such as once a day. Certain animals send out signals to the others that they will soon go to sleep. Yawning is such a signal.

Both humans and many animals sleep about once a day. Some animals, such as cats, sleep many times a day for short periods.

When people sleep they often have dreams. Probably some animals do, too.

Not only people sleep, all mammals and birds, and most fish, reptiles and other animals do, too.

Brief stages of sleep[change | change source]

There are 4 stages during sleep:

1. Stage 1: The lightest sleep of NREM (Non-Rapid Eye Movement) sleep which is the process of falling asleep.
2. Stage 2: The first elucidated stage of NREM sleep; the beginning of falling asleep including regular breathing and heart rates, the body temperature dropping, and becoming disconnected with the environment.
3. Stages 3: Deep NREM sleep which involves delta waves or slow waves. It is difficult to wake one up in the course of this stage as they are in deep sleep. Common disorders that occur during this stage are sleep walking and talking.
4. Stage 4: The dreaming stage and brain waves are more vigorous with rapid eye movement. Awakenings are more common in REM (Rapid Eye Movement) sleep as opposed to NREM.

Sleeping is associated with a state of muscle relaxation and limited perception of environmental stimuli.

While humans sleep, REM and NREM are sleep patterns that help with long term memory, remembering information, procedural memory, and creative thinking.

Different types of sleep

REM sleep

In mammals and birds, sleep can be divided into two categories. In one of them, the eyes move rapidly. It is called REM-sleep (from rapid eye movement). Most dreams take place in this phase as well as energy from the brain to the body progressing, the body becoming relaxed, and the eyes dashing back and forth while sleeping. This phase helps prepare one with vitality for performance in the next day. REM-sleep occurs normally at intervals throughout the night, and the periods of REM-sleep increase in length in the second half of the night. It is often encountered 90 minutes after falling asleep and continues to occur every 90 minutes. REM-sleep was first discovered in 1952-53.

REM sleep is found in mammals and songbirds, but is "poorly established" in reptiles and fish. A survey suggests:

"This remarkable similarity of characteristics may have resulted from a convergent evolution in mammals and songbirds".

NREM sleep

The other category, where this movement of the eyes does not happen, is called NREM-sleep (Non-REM sleep). Usually, dreams do not occur during this time. There are three or four stages of NREM-sleep. Stage I is just barely sleeping, or dozing. Stage II is also light sleep. Normally, in adult humans, about half of the time spent asleep is spent in light sleep. Stages III and IV are called deep sleep. Deep sleep is necessary for growth and healing. It can be quite difficult to awaken someone who is in stage III or stage IV sleep. Sometimes stages III and IV are combined and called stage III.

Adult humans normally sleep in cycles of 90 to 110 minutes each. The night's sleep can be 4 or 5 of these cycles. Each cycle includes, in this order: stage I, stage II, stage III (IV), and REM.

Getting enough sleep

People who receive less than 8 hours of sleep a night tend to complain more and feel very fatigued throughout the day. Receiving the appropriate amount of sleep is extremely important as it could affect one’s body and increase the chances of serious health problems.

- Toddlers (4 to 12 months): 12 to 16 hours (w/ naps)

- Toddlers (1-2 years): 11 to 14 hours (w/ naps)

- Preschoolers (3-5 years): 10 to 13 hours (w/ naps)

- Grade Schoolers (6 to 12 years): 9 to 12 hours

- Teenagers(13-18 years): 8 to 10 hours

- Adults (including old age): 7 to 9 hours

Effect of chronic sleep loss

Insufficient sleep has been linked to the development and management of a number of chronic diseases such as type 2 diabetes, cardiovascular disease, obesity, and depression.

Sleeping problems

A good night’s sleep is extremely important for one’s quality of life. People may have trouble going to sleep, staying asleep or getting enough sleep. This usually means that they are too sleepy in the daytime.

There are many things that influence sleep. Also some substances, called stimulants – coffee is an example – can cause poor sleep. When people have just eaten something, the body is busy digesting what they have ate. This can cause poor sleep, too. Worrying and stress can cause poor sleep.

There are many diseases that cause poor sleep. Fever can lead to bad dreams. Poor sleep can be a side effect of some medications.

Sleep disorders directly influence how a person sleeps. Examples of sleep disorders are narcolepsy, sleep apnea and circadian rhythm sleep disorders.

The 4 most common sleep disorders as noted below:

- Insomnia which consists of difficulties going to sleep at night, having no energy, waking up often in the middle of the night, waking up earlier than planned, and changing mood behaviors.

- Sleep Apnea which is due to the lack of breathing for several seconds which results in the brain awakening and forcing a respiratory effect to breathe harder. As a result of the multiple occurrences during the night, the body cannot go back to sleep, leading to fatigue.

- Restless Leg Syndrome is a need to move one’s leg while resting. While having the urge to move your feet during the night, this may affect the ability to fall and stay asleep.

- Narcolepsy, the inability to control the brain’s sleep/wakefulness cycle which leads to daytime sleepiness and falling asleep at unexpected times.

Tips for better sleep

Some habits that can improve your sleep health:

• Be consistent. Go to bed at the same time each night and get up at the same time each morning, including on the weekends
• Make sure your bedroom is quiet, dark, relaxing, and at a comfortable temperature
• Remove electronic devices, such as TVs, computers, and smart phones, from the bedroom
• Avoid large meals, caffeine, and alcohol before bedtime
• Get some exercise. Being physically active during the day can help you fall asleep more easily at night.

Latest articles - Sleep

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Sleep on Wikipedia

• Wikipedia's article on Sleep
• American Academy of Sleep Medicine
• National Sleep Foundation
• World Sleep Foundation
• National Center on Sleep Disorders Research