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a period of rest for the body and mind, during which volition and consciousness are in partial or complete abeyance and the bodily functions partially suspended. Sleep has also been described as a behavioral state marked by characteristic immobile posture and diminished but readily reversible sensitivity to external stimuli.

NREM and REM Sleep. Prior to the discovery and reporting of rapid eye movements during sleep, it was thought that sleep was a single state of passive recuperation in which the central nervous system was deactivated. Studies concerned with the measurement of central and autonomic activities during sleep have led to its division into two types: non–rapid eye movement (NREM) sleep, also called orthodox or synchronized (S) sleep; and rapid eye movement (REM) sleep (so called because of the rapid eye movements during this stage), also called paradoxical or desynchronized (D) sleep.

On the basis of electroencephalographic (EEG) criteria, NREM sleep is subdivided into four stages. Stage 1 is observed immediately after sleep begins or after momentary arousals and is characterized by low-voltage, mixed-frequency EEG tracing, with predominantly theta-wave activity (four to seven hertz, that is, cycles per second). Stage 2 is characterized by intermittent waves of 12 to 16 hertz, known as sleep spindles.Stages 3 and 4 consist of relatively high voltage EEG tracings with a predominance of delta wave activity (one to two hertz).

The EEG patterns of NREM sleep suggest that this is the kind of apparently restful state that supports the recuperative functions assigned to sleep. NREM sleep is increased after physical activity and has a relatively high priority among humans in the recovery sleep following extended periods of wakefulness.

Within 90 minutes after sleep begins, an adult progresses through all four stages of NREM sleep and then proceeds into the first of a series of REM periods of sleep. Brief cycles of about 10 to 30 minutes of REM sleep recur throughout the night, alternating with various stages of NREM sleep. With each cycle, NREM sleep decreases and REM sleep increases so that by the end of the night most of the sleep is REM sleep, which is when dreams occur. While everyone dreams every night, many do not remember dreaming; most people are aware, however, that they dream more just before rising.

In addition to the rapid eye movements that can be observed through closed eyelids, REM sleep can be recognized by complete relaxation of the lower jaw. Convulsions, myocardial infarction, and cardiac arrhythmias are more likely to occur during REM sleep. This is probably because of increased autonomic activity, irregular pulse, and fluctuations in blood pressure, which are all typical of REM sleep.
Patterns of Sleep. Although the average adult spends approximately 25 percent of total accumulated sleep in REM sleep and 75 percent in NREM sleep, the cyclic changes vary with individuals. The pattern of sleep, in addition to the REM and NREM states, also includes the periods of sleep and wakefulness within a 24-hour period.

Factors affecting the total sleep pattern include age, state of physical health, psychological state, and certain drugs. Newborns follow a pattern of several hours of sleep followed by a period of wakefulness. REM sleep occurs at the onset of sleep in infants; it rarely does in adults. As the child matures there is an increasing tendency toward longer periods of nocturnal sleep. Elderly persons sometimes return to the shorter periods of sleep that are typical of infants.
Benefits of Sleep. Sleep requirements vary greatly among individuals. Infants usually require 16 to 20 hours of total sleep during a 24-hour period, and the amount decreases as the child matures. An adult usually requires 6 to 9 hours of total sleep, and requirements continue to decrease with aging.

Most theorists agree that sleep has value as a recuperative and adaptive function in the lives of humans. The relatively high metabolic needs of mammals and birds to maintain a constant body temperature in a wide range of environmental temperatures suggests that the periodic decreases in metabolic rate and body temperature that occur in NREM sleep allow for recuperation and restitution of body tissues. For example, even though the function of stage 2 NREM sleep is not clear, approximately half of human sleep time is spent in this stage. It is also theorized that REM sleep provides a period of recuperation of mental activities and preparation for wakefulness. During REM sleep it is believed that there is increased metabolic activity in the brain so that during waking hours it is more receptive to new information and can assimilate it more easily.
sleep apnea syndrome episodes of apnea (cessation of breathing) occurring at the transition from NREM to REM sleep, with repeated wakening and excessive daytime sleepiness; it occurs most often in middle-aged, obese males and is thought to have several causes, one being collapse or obstruction of the airway with the inhibition of muscle tone that characterizes REM sleep. The condition is arbitrarily defined as more than five cessations of airflow for at least 10 seconds each per hour of sleep.
sleep disorders chronic disorders involving sleep; primary sleep disorders are classified as dyssomnias or parasomnias. Among the minor disorders are sleepwalking, sleeptalking, enuresis, bruxism (tooth grinding), and nightmares. Sleepwalking is not considered serious if it occasionally occurs in childhood. It should be considered pathological, however, if it persists into adulthood. Sleeptalking is common to many persons and, while it may annoy others whose sleep it may disturb, it is not considered pathological.

A sleep disorder occurring in early childhood, and not to be confused with nightmares, is sleep terror disorder. The child awakens with a scream, is in panic and cannot be consoled, and often is incoherent; the following morning, there is poor recall of the event. Treatment usually involves reassurance of the parents. Adults who experience night terrors often have some psychological problem requiring treatment. More serious disorders of sleep include persistent insomnia, narcolepsy, and chronic hypersomnia. Hypersomnia can occur with central nervous system damage or may be secondary to some physical and mental illnesses, particularly depression.
sleep terror disorder a sleep disorder of the parasomnia group, consisting of repeated episodes of pavor nocturnus (sleep terrors).




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.).
[A.S. slaep]


(slēp) a period of rest for the body and mind, during which volition and consciousness are in abeyance and bodily functions are partially suspended; also described as a behavioral state, with characteristic immobile posture and diminished but readily reversible sensitivity to external stimuli.
NREM sleep  non-rapid eye movement sleep; the deep, dreamless period of sleep during which the brain waves are slow and of high voltage, and autonomic activities, such as heart rate and blood pressure, are low and regular.
REM sleep  the period of sleep during which the brain waves are fast and of low voltage, and autonomic activities, such as heart rate and respiration, are irregular. This type of sleep is associated with dreaming, mild involuntary muscle jerks, and rapid eye movements (REM). It usually occurs three to four times each night at intervals of 80 to 120 minutes, each occurrence lasting from 5 minutes to more than an hour.


A natural periodic state of rest for the mind and body, in which the eyes usually close and consciousness is completely or partially lost, so that there is a decrease in bodily movement and responsiveness to external stimuli. During sleep the brain undergoes a characteristic cycle of brain-wave activity that includes intervals of dreaming.
To be in the state of sleep.


Etymology: AS, slaepan, to sleep
a state marked by reduced consciousness, diminished activity of the skeletal muscles, and depressed metabolism. People normally experience sleep in patterns that follow four observable, progressive stages. A device such as an encephalograph is used to record the recurrent pattern of brain waves during the stages. During stage 1 the brain waves are of the theta type, followed in stage 2 by the appearance of distinctive sleep spindles; during stages 3 and 4 the theta waves are replaced by delta waves. These four stages represent three fourths of a period of typical sleep and collectively are called nonrapid eye movement sleep. The remaining time is usually occupied with rapid eye movement (REM) sleep, which can be detected with electrodes placed on the skin around the eyes so that tiny electric discharges from contractions of the eye muscles are transmitted to recording equipment. The REM sleep periods, lasting from a few minutes to half an hour, alternate with the NREM periods. Dreaming occurs during REM time. Individual sleep patterns normally change throughout life because daily requirements for sleep gradually diminish from as much as 20 hours a day in infancy to as little as 6 hours a day in old age. Infants tend to begin a sleep period with REM sleep, whereas REM activity usually follows the four stages of NREM sleep in adults.


a nursing outcome from the Nursing Outcomes Classification (NOC) defined as natural periodic suspension of consciousness during which the body is restored. See also Nursing Outcomes Classification.


Rest resulting from a natural suspension of voluntary bodily functions and consciousness. Good sleep hygiene is regarded as a component of good health: it enhances the immune system, and is beneficial for common colds, cardiovascular disease, longevity, recuperation from injuries and productivity.


Sleep disorders Rest resulting from a natural suspension of voluntary bodily functions and consciousness. See Deep sleep, Delta sleep, Good habit, Light sleep, Microsleep, Non-REM sleep, Nocturnal sleep, Normal sleep, REM sleep, Twilight sleep. Cf Bad habit, Poor sleeping hygiene.


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), electroencephalographic characteristics (delta waves, synchronization), physiologic characteristics, and presumed anatomic level (pontine, mesencephalic, rhombencephalic, rolandic).
[A.S. slaep]


The natural, regular, daily state of reduced consciousness and METABOLISM that occupies about one-third of the average person's life. Sleep requirements vary considerably in health, between about 4 and 10 hours in each 24 hour period. The purpose of sleep is unknown but prolonged deprivation is harmful, causing depression and mental disturbances, including hallucinations.


Physiologic state of relative unconsciousness and inaction of voluntary muscles, its need recurs periodically.
[A.S. slaep]


a period of rest during which volition and consciousness are in partial or complete abeyance and the bodily functions partially suspended; a behavioral state marked by characteristic immobile posture and diminished but readily reversible sensitivity to external stimuli.

sleep deprivation
caused in animals by constant stimulation, e.g. preventing them from lying down, is followed by a compensatory period of prolonged sleep whenever the opportunity arises.
sleep disorders
put to sleep
a common euphemism for euthanasia.
rapid eye movement sleep
that type of sleep characterized by low voltage but fast electroencephalographic activity and little muscular activity except of the ocular muscles. Believed to be the critical or necessary component of sleep. Called also 'sleep of the body' and paradoxical sleep. Called also REM.

Patient discussion about sleep

Q. How to deal with sleeping problems? I wonder if anyone could help me. Here's the thing: I’ve been in school break for two months now and that means i usually go to bed at about 2 am, and I usually wake up with an alarm clock at 11 for breakfast then lunch immediately after breakfast. My problem is that I have problems sleeping, I usually stay an hour or two in bed trying to get some sleep.

A. My Dr. has me on Ambien cr,12.5 MG Tablets, and they work fine for me. I though i would see if they really worked about a month ago and did not take a pill before bed time, and i went right to sleep and slep for about 1 1/2 hrs and was awake the rest of the night, so i never fail to take a tablet every night when i lay down. Ask your dr. about this med.

Q. I go to sleep & use to wake up paralyzed in my sleep. I go to sleep & use to wake up paralyzed in my sleep. But not asleep, just laying there, eyes wide open paralyzed. I couldn't breath, I couldn't speak, move anything but my eyes. I could look around but I couldn't even breathe. This has happened a few times in my old house, once in my mother's house (she lived by the side of a graveyard), and then only once in my new house. What is it and what do you think is causing it?

A. I had the same problem but never at night...and it only happened during the day when I take nap. I will wake up and I can't move or talk, I can't open my eyes either. I've never been able to snap out of it though, I just have to lay there until I go back to sleep, and usually it doesn't happen when I wake up the next time. Needless to say I try NOT to take naps anymore, because it happens nearly every time.

Q. sleeping problems i"m waking up in the middle of the night and can't get back.

A. The first steps usually recommended are to improve sleep hygiene:
• Sleep only as much as you need to feel rested
• Keep a regular sleep schedule
• Avoid forcing sleep
• Exercise regularly for at least 20 minutes, preferably 4 to 5 hours before bedtime
• Avoid caffeinated beverages after lunch
• Avoid alcohol near bedtime: no "night cap"
• Avoid smoking, especially in the evening
• Do not go to bed hungry
• Adjust bedroom environment
• Deal with your worries before bedtime
These practices address many of the causes of sleep problems. However, sleep problems may result from many causes, so consulting a doctor may be wise.

Take care,

More discussions about sleep
References in periodicals archive ?
Lack of sleep is a growing problem in the United States, Carskadon says.
The study confirms previous results and shows that Sublinox (OX 22), in addition to fast sleep induction, offers patients with sleeping disturbances good and maintained sleep without 'day-after'- residual effects.
Teach yourself that routine, and your body will know it's time to sleep.
Van Cauter and other researchers discussed possible links between sleep deprivation, expanding waistlines, and obesity-related problems this week in Washington, D.
If keeping cool and fatigue management aren't working, try some of the sleep strategies in the box on page 64 and talk with your doctor about the possibility of a sleep disorder.
We now sleep less than people in any other industrialized country.
When sleep scientists at the University of Chicago restricted a group of volunteers to four hours of sleep a night over six-days, the participants' leptin levels plunged.
Regular exercise is always prescribed as one of the three major cornerstones of good sleep hygiene.
In some animals, like dolphins and whales, only half of the brain is at rest during sleep.
Behaviorally, sleep is a reversible state, different from wakefulness, characterized by perceptual disengagement from, and lack of responsiveness to, the environment.
Given the strong interest in sleep medicine by Otolaryngologists at a number of university-based centers and by a cadre of Otolaryngology practitioners who have expanded beyond the surgical management of sleep disorders to disease evaluation and medical management, the OTO RRC petitioned to be included in the discussions about Sleep Medicine.