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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.
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.
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.
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(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.
sleepRest 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.
sleepSleep 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.
sleepThe 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.
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.
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?
Q. sleeping problems i"m waking up in the middle of the night and can't get back.
• 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.