Sleep is a naturally recurring altered state of consciousness An altered state of consciousness, , also named altered state of mind, is any condition which is significantly different from a normal waking beta wave state. The expression was used as early as 1969 by Charles Tart and describes induced changes in one's mental state, almost always temporary. A synonymous phrase is "altered states of with relatively suspended sensory and motor activity, characterized by the inactivity of nearly all voluntary muscles Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system. It is one of three major muscle types, the others being cardiac and smooth muscle. As its name suggests, most skeletal muscle is attached to bones by bundles of collagen fibers known as tendons.[1] It is distinguished from quiet wakefulness Wakefulness is a daily recurring brain state in which an individual is conscious and engages in coherent cognitive and behavior responses to the external world such as communication, ambulation, nutritional ingestion and procreation. Being awake is the opposite of being asleep in which most external inputs to the brain are excluded from neural by a decreased ability to react to stimuli In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction. A stimulus is often the first component of a homeostatic, but it is more easily reversible than hibernation Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food is short, tapping energy reserves, body fat, at a slow rate. It is the animal's slowed metabolic rate which leads to a or coma In medicine, a coma is a profound state of unconsciousness. A person in a coma cannot be awakened, fails to respond normally to pain, light or sound, does not have sleep-wake cycles, and does not take voluntary actions. A person in a state of coma can be described as comatose. Sleep is a heightened anabolic Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or as 'catabolic', which is the opposite. Anabolism is powered by catabolism, where large molecules are broken down state, accentuating the growth and rejuvenation of the immune, nervous, skeletal and muscular systems. It is observed in all mammals, all birds, and many reptiles, amphibians, and fish.
The purposes and mechanisms of sleep are only partially clear and are the subject of intense research.[2]
Contents |
Physiology
Sleep stages
In mammals and birds, sleep is divided into two broad types: rapid eye movement Rapid Eye Movement sleep is a normal stage of sleep characterized by the rapid movement of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Kleitman and Aserinsky in the early 1950s (REM) and non-rapid eye movement The sleep stages 1 through 3, previously known as stages 1 through 4, are collectively referred to as NREM, non-rapid eye movement, sleep. Rapid eye movement is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement during this stage (NREM or non-REM) sleep. Each type has a distinct set of associated physiological, neurological, and psychological features. The American Academy of Sleep Medicine The American Academy of Sleep Medicine is a United States professional society for the medical subspecialty of sleep medicine. It was established in 1975. The (AASM) is the only professional society that is dedicated exclusively to the medical subspecialty of sleep medicine. As the leading voice in the field of sleep medicine, the AASM sets (AASM) further divides NREM into three stages: N1, N2, and N3, the last of which is also called delta A delta wave is a high amplitude brain wave with a frequency of 1–4 hertz which can be recorded with an electroencephalogram and is usually associated with slow-wave sleep (SWS) sleep or slow-wave sleep Slow-wave sleep , often referred to as deep sleep, consists of stages three and four of non-rapid eye movement sleep, according to the Rechtschaffen & Kales (R&K) standard of 1968. As of 2008, the American Academy of Sleep Medicine (AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3 (SWS).[3]
Sleep cycles through the night, with deep sleep early on and more REM (marked in red) toward morning. Stage N3 sleep; EEG Electroencephalography is the recording of electrical activity along the scalp produced by the firing of neurons within the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp. In highlighted by red box. Thirty seconds of deep sleep, here with greater than 50% delta waves. REM sleep Rapid Eye Movement sleep is a normal stage of sleep characterized by the rapid movement of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Kleitman and Aserinsky in the early 1950s; EEG highlighted by red box; eye movements highlighted by red line. Thirty seconds of sleep.Sleep proceeds in cycles of REM and NREM, the order normally being N1 → N2 → N3 → N2 → REM. There is a greater amount of deep sleep (stage N3) early in the night, while the proportion of REM sleep increases later in the night and just before natural awakening.
The stages of sleep were first described in 1937 by Alfred Lee Loomis Alfred Lee Loomis was an American attorney, investment banker, physicist, philanthropist and patron of scientific research. He established the Loomis Laboratory in Tuxedo Park, New York, and his role in the development of radar is considered instrumental in the Allied victory in World War II. He invented the Aberdeen Chronograph for measuring and his coworkers, who separated the different electroencephalography Electroencephalography is the recording of electrical activity along the scalp produced by the firing of neurons within the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp. In (EEG) features of sleep into five levels (A to E), which represented the spectrum from wakefulness to deep sleep.[4] In 1953, REM sleep was discovered as distinct, and thus William Dement William Charles Dement , is a pioneering US sleep researcher, and founder of the Sleep Research Center, the world's first sleep laboratory, at Stanford University. He is a leading authority on sleep, sleep deprivation, and the diagnosis and treatment of sleep disorders such as sleep apnea and narcolepsy and Nathaniel Kleitman Nathaniel Kleitman was Professor Emeritus in Physiology at the University of Chicago. Author of the seminal 1939 book Sleep and Wakefulness, he is recognized as the father of American sleep research. Kleitman, along with his student Eugene Aserinsky, was the first to discover rapid eye movement (REM) sleep and demonstrate that it was correlated reclassified sleep into four NREM stages and REM.[5] The staging criteria were standardized in 1968 by Allan Rechtschaffen Allan Rechtschaffen is a noted pioneer in the field of sleep research whose work includes some of the first laboratory studies of insomnia, narcolepsy, and napping and Anthony Kales in the "R&K sleep scoring manual."[6] In the R&K standard, NREM sleep was divided into four stages, with slow-wave sleep comprising stages 3 and 4. In stage 3, delta waves made up less than 50% of the total wave patterns, while they made up more than 50% in stage 4. Furthermore, REM sleep was sometimes referred to as stage 5.
In 2004, the AASM commissioned the AASM Visual Scoring Task Force to review the R&K scoring system. The review resulted in several changes, the most significant being the combination of stages 3 and 4 into Stage N3. The revised scoring was published in 2007 as The AASM Manual for the Scoring of Sleep and Associated Events.[7] Arousals and respiratory, cardiac, and movement events were also added.[8][9]
Sleep stages and other characteristics of sleep are commonly assessed by polysomnography Polysomnography , also known as a sleep study, is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Greek πολύς (polus for "many, much", indicating many channels), the in a specialized sleep laboratory. Measurements taken include EEG of brain waves, electrooculography Electrooculography is a technique for measuring the resting potential of the retina. The resulting signal is called the electrooculogram. The main applications are in ophthalmological diagnosis and in recording eye movements. Unlike the electroretinogram, the EOG does not represent the response to individual visual stimuli (EOG) of eye movements, and electromyography Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or (EMG) of skeletal muscle Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system. It is one of three major muscle types, the others being cardiac and smooth muscle. As its name suggests, most skeletal muscle is attached to bones by bundles of collagen fibers known as tendons activity. In humans, each sleep cycle lasts from 90 to 110 minutes on average,[10] and each stage may have a distinct physiological function. This can result in sleep that exhibits loss of consciousness Unconsciousness, more appropriately referred to as loss of consciousness or lack of consciousness, is a dramatic alteration of mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is an illustration of unconsciousness. Fainting due to a drop in but does not fulfill its physiological functions (i.e., one may still feel tired after apparently sufficient sleep).
NREM sleep
Main article: Non-rapid eye movement sleep The sleep stages 1 through 3, previously known as stages 1 through 4, are collectively referred to as NREM, non-rapid eye movement, sleep. Rapid eye movement is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement during this stageAccording to the 2007 AASM standards, NREM consists of three stages. There is relatively little dreaming in NREM.
Stage N1 refers to the transition of the brain from alpha waves Alpha waves are electromagnetic oscillations in the frequency range of 8–12 Hz arising from synchronous and coherent electrical activity of thalamic pacemaker cells. They are also called Berger's wave in memory of the founder of EEG having a frequency of 8 to 13 Hz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applications (common in the awake state) to theta waves A theta rhythm is an oscillatory pattern in EEG signals recorded either from inside the brain or from electrodes glued to the scalp. Two types of theta rhythm have been described. The "hippocampal theta rhythm" is a strong oscillation that can be observed in the hippocampus and other brain structures in numerous species of mammals having a frequency of 4 to 7 Hz. This stage is sometimes referred to as somnolence or drowsy sleep. Sudden twitches and hypnic jerks A hypnic or hypnagogic jerk is an involuntary myoclonic twitch which occurs during hypnagogia, just as the subject is beginning to fall asleep. Physically, hypnic jerks resemble the "jump" made when a person is startled, also known as positive myoclonus Myoclonus is brief, involuntary twitching of a muscle or a group of muscles. It describes a medical sign and, generally, is not a diagnosis of a disease. The myoclonic twitches are usually caused by sudden muscle contractions; they also can result from brief lapses of contraction. Contractions are called positive myoclonus; relaxations are called, may be associated with the onset of sleep during N1. Some people may also experience hypnagogic hallucinations Hypnagogia , often misspelled hypnogogia, is a term coined by Alfred Maury for the transitional state between wakefulness and sleep during this stage, which can be troublesome to them. During N1, the subject loses some muscle tone In physiology, medicine, and anatomy, muscle tone is the continuous and passive partial contraction of the muscles. It helps maintain posture, and it declines during REM sleep. It is not to be confused with the concept of toning in physical exercise and most conscious awareness of the external environment.
Stage N2 is characterized by sleep spindles A sleep spindle is a burst of brain activity visible on an EEG that occurs during stage 2 sleep. It consists of 12-16 Hz waves that occur for 0.5 to 1.5 seconds ranging from 11 to 16 Hz (most commonly 12–14 Hz) and K-complexes A K-complex is an electroencephalography waveform that occurs during stage 2 of NREM sleep. It is the "largest event in healthy human EEG". They are more frequent in the first sleep cycles of sleep. During this stage, muscular activity as measured by EMG decreases, and conscious awareness of the external environment disappears. This stage occupies 45% to 55% of total sleep in adults.
Stage N3 (deep or slow-wave sleep Slow-wave sleep , often referred to as deep sleep, consists of stages three and four of non-rapid eye movement sleep, according to the Rechtschaffen & Kales (R&K) standard of 1968. As of 2008, the American Academy of Sleep Medicine (AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3) is characterized by the presence of a minimum of 20% delta waves A delta wave is a high amplitude brain wave with a frequency of 1–4 hertz which can be recorded with an electroencephalogram and is usually associated with slow-wave sleep (SWS) ranging from 0.5 to 2 Hz and having a peak-to-peak amplitude >75 μV. (EEG standards define delta waves to be from 0 – 4 Hz, but sleep standards in both the original R&K, as well as the new 2007 AASM guidelines have a range of 0.5 – 2 Hz.) This is the stage in which parasomnias Parasomnias are a category of sleep disorders that involve abnormal and unnatural movements, behaviors, emotions, perceptions, and dreams that occur while falling asleep, sleeping, between sleep stages, or during arousal from sleep. Most parasomnias are dissociated sleep states which are partial arousals during the transitions between wakefulness such as night terrors A night terror, also known as a sleep terror or pavor nocturnus, is a parasomnia disorder characterized by extreme terror and a temporary inability to regain full consciousness. The subject wakes abruptly from slow-wave sleep, with waking usually accompanied by gasping, moaning, or screaming while waking. It is often impossible to awaken the, nocturnal enuresis Bedwetting is involuntary urination while asleep after the age at which bladder control would normally be anticipated. The medical term for this condition is "nocturnal enuresis." Primary nocturnal enuresis is when a child has not yet stayed dry on a regular basis. Secondary nocturnal enuresis (SNE) is when a child or adult begins, sleepwalking Sleepwalking, also known as somnambulism, is a sleep disorder belonging to the parasomnia family. Sleepwalkers arise from the slow wave sleep stage in a state of low consciousness and perform activities that are usually performed during a state of full consiousness. These activities can be as benign as sitting up in bed, walking to the bathroom,, and somniloquy Somniloquy or sleep-talking is a parasomnia that refers to talking aloud in one's sleep. It can be quite loud, ranging from simple sounds to long speeches, and can occur many times during sleep. Listeners may or may not be able to understand what the person is saying occur. Many illustrations and descriptions still show a stage N3 with 20%-50% delta waves and a stage N4 with greater than 50% delta waves; these have been combined as stage N3.
REM sleep
Main article: Rapid eye movement sleep Rapid Eye Movement sleep is a normal stage of sleep characterized by the rapid movement of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Kleitman and Aserinsky in the early 1950sRapid eye movement sleep, or REM sleep, accounts for 20%–25% of total sleep time in most human adults. The criteria for REM sleep include rapid eye movements as well as a rapid low-voltage EEG. Most memorable dreaming occurs in this stage. At least in mammals, a descending muscular atonia In medicine, atony refers to a muscle that has lost its strength. It is frequently associated with the conditions Atonic seizure, atonic colon, uterine atony, gastrointestinal atony (occurs postoperatively) and choreatic atonia is seen. Such paralysis may be necessary to protect organisms from self-damage through physically acting out scenes from the often-vivid dreams that occur during this stage.
Timing
The human biological clockSleep timing is controlled by the circadian clock A circadian rhythm is a roughly 24-hour cycle in the biochemical, physiological, or behavioural processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian" comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day". The, sleep-wake homeostasis Homeostasis is the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition. Typically used to refer to a living organism, the concept came from that of milieu interieur that was created by Claude Bernard and published in 1865. Multiple dynamic equilibrium adjustment, and in humans, within certain bounds, willed behavior. The circadian clock—an inner timekeeping, temperature-fluctuating, enzyme-controlling device—works in tandem with adenosine Adenosine is a nucleoside composed of a molecule of adenine attached to a ribose sugar molecule moiety via a β-N9-glycosidic bond, a neurotransmitter that inhibits many of the bodily processes associated with wakefulness. Adenosine is created over the course of the day; high levels of adenosine lead to sleepiness. In diurnal Diurnality is an animal behavior characterized by activity during the day and sleeping at night. Animals that are not diurnal might be nocturnal or crepuscular (active primarily during twilight, i.e., at dusk and dawn). Many animal species are diurnal, including many mammals, insects, reptiles and birds. The diurnal pattern is often controlled animals, sleepiness occurs as the circadian element causes the release of the hormone melatonin Melatonin (pronounced /ˌmɛləˈtoʊnɪn/ ), also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes. In animals, circulating levels of the hormone melatonin vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions and a gradual decrease in core body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. This process is one aspect of homeostasis: a dynamic state of stability between an animal's internal environment and its external environment . If the body is unable to maintain a normal. The timing is affected by one's chronotype Chronotype is an attribute of human beings reflecting whether they are alert and prefer to be active early or late in the day. The continuum is often referred to as "morningness/eveningness" or "larks" and "owls" where morning people wake up early and are most alert in the first part of the day, and evening people are. It is the circadian rhythm that determines the ideal timing of a correctly structured and restorative sleep episode.[11]
Homeostatic sleep propensity (the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep.[12] Along with corresponding messages from the circadian clock, this tells the body it needs to sleep.[13] Sleep offset (awakening) is primarily determined by circadian rhythm. A person who regularly awakens at an early hour will generally not be able to sleep much later than his or her normal waking time, even if moderately sleep-deprived.
Sleep duration is affected by the gene DEC2. Some people have a mutation of this gene; they sleep two hours less than normal. Neurology professor Ying-Hui Fu and her colleagues bred mice that carried the DEC2 mutation and slept less than normal mice.[14][15]
|
Wed, 01 Sep 2010 15:52:12 GMT+00:00
Softpedia The Sleep /Wake button has shifted from the top left of the device over to the top right, mimicing [sic] its placement on the iPhone family. ... Next generation iPod touch details surface: thinner, 3G and VoIP capable? AllNewsMac (press release) Binary Boys: An extreme tech makeover: AppleTV edition Rocky Mountain Collegian Apple iPod Touch Features Retina Display and A4 Processor SlashGear (blog) TheAppleBlog (blog)
480px x 640px | 30.10kB
[source page]
http i272 photobucket com albums jj178 moonfeen Other Sleep jpg 2009 06 19 01 00 05
Sun, 05 May 2002 17:00:00 PDT
Helen West Casebook: Deep Sleep (Season 1, Episode 1): When the wife of a respected pharmacist dies in her sleep, it seems like natural causes ... amazon.com.
