Stages of sleep
Stages of sleep
Non REM sleep (NREM), which accounts for 75-80% of total sleep time: Stage 1, with an elimination in alpha waves compared to awake resting with eyes closed. The stage is sometimes referred to as somnolence, or "drowsy sleep". It appears at sleep onset (as it is mostly a transition state into Stage 2), and can be associated with so-called hypnagogic hallucinations. In this period, the subject loses some muscle tone, and conscious awareness of the external environment: Stage 1 can be thought of as a gateway state between wake and sleep. Stage 2, with "sleep spindles" (12–16 Hz) and "K-complexes". The EMG lowers, and conscious awareness of the external environment all but disappears. This occupies 45-55% of total sleep. Stage 3, with delta waves, also called delta rhythms (1–2 Hz) is considered part of SWS and functions primarily as a transition into stage four. Overall it occupies 3-8% of total sleep time. Stage 4 is true delta sleep. It predominates the first third of the night and accounts for 10-15% of total sleep time. This is often described as the deepest stage of sleep; it is exceedingly difficult to wake a subject in this state. This is the stage in which night terrors and sleepwalking occur. Stage 5, or Rapid eye movement (REM) sleep, associated with dreaming, especially bizarre, visual, and seemingly random dreams. REM sleep is predominant in the final third of a sleep period, its timing linked to circadian rhythm and body temperature. The EEG in this period is aroused and looks similar to stage 1. Sleep proceeds in cycles of NREM and REM phases. In humans, the cycle of REM and NREM is approximately 90 minutes. Each stage may have a distinct physiological function. Drugs such as alcohol and sleeping pills can suppress certain stages of sleep (see sleep deprivation below). This can result in a sleep that exhibits loss of consciousness but does not fulfill its physiological functions.
Each sleep stage is not necessarily uniform. Within a given stage, a cyclical alternating pattern may be observed.
Theories regarding the function of sleepRestorative theories of sleep describe sleep as a dynamic time of healing and growth for organisms. For example, during stages 3 and 4, or slow wave sleep, growth hormone levels increase, and changes in immune function occur. The myriad illnesses associated with sleep deprivation testify to its restorative function.
According to the Ontogenetic Hypothesis of REM sleep, the activity occurring during neonatal REM sleep (or Active Sleep) seems to be particularly important to the developing organism (Marks et al., 1995). Studies investigating the effects of Active Sleep deprivation have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass (Mirmiran et al. 1983), and an abnormal amount of neuronal cell death (Morrissey, Duntley & Anch, 2004). Given sleep's heterogeneous nature, however, no single theory predominates as it is difficult to describe one single "function" of sleep.
One process known to be highly dependent on sleep is memory. REM sleep appears to help with the consolidation of spatial and procedural memory, while Slow-wave sleep helps with the consolidation of declarative memories. When experimental subjects are given academic material to learn, especially if it involves organized, systematic thought, their retention is markedly increased after a night's sleep. Mere rote memorization is retained similarly well without an intervening period of sleep.
Non-REM sleep is an anabolic state marked by physiological processes of growth and rejuvenation of the organism's immune, nervous, muscular, and skeletal systems. Sleep also restores neurons and increases production of brain proteins and certain hormones. Wakefulness may perhaps be viewed as a cyclical, temporary, hyperactive catabolic state during which the organism acquires nourishment and procreates. Asking the question "Why do we awaken?" instead of "Why do we sleep?" yields a different perspective toward understanding how sleep and its stages contribute to a healthy organism.
Non REM sleep (NREM), which accounts for 75-80% of total sleep time: Stage 1, with an elimination in alpha waves compared to awake resting with eyes closed. The stage is sometimes referred to as somnolence, or "drowsy sleep". It appears at sleep onset (as it is mostly a transition state into Stage 2), and can be associated with so-called hypnagogic hallucinations. In this period, the subject loses some muscle tone, and conscious awareness of the external environment: Stage 1 can be thought of as a gateway state between wake and sleep. Stage 2, with "sleep spindles" (12–16 Hz) and "K-complexes". The EMG lowers, and conscious awareness of the external environment all but disappears. This occupies 45-55% of total sleep. Stage 3, with delta waves, also called delta rhythms (1–2 Hz) is considered part of SWS and functions primarily as a transition into stage four. Overall it occupies 3-8% of total sleep time. Stage 4 is true delta sleep. It predominates the first third of the night and accounts for 10-15% of total sleep time. This is often described as the deepest stage of sleep; it is exceedingly difficult to wake a subject in this state. This is the stage in which night terrors and sleepwalking occur. Stage 5, or Rapid eye movement (REM) sleep, associated with dreaming, especially bizarre, visual, and seemingly random dreams. REM sleep is predominant in the final third of a sleep period, its timing linked to circadian rhythm and body temperature. The EEG in this period is aroused and looks similar to stage 1. Sleep proceeds in cycles of NREM and REM phases. In humans, the cycle of REM and NREM is approximately 90 minutes. Each stage may have a distinct physiological function. Drugs such as alcohol and sleeping pills can suppress certain stages of sleep (see sleep deprivation below). This can result in a sleep that exhibits loss of consciousness but does not fulfill its physiological functions.
Each sleep stage is not necessarily uniform. Within a given stage, a cyclical alternating pattern may be observed.
Theories regarding the function of sleepRestorative theories of sleep describe sleep as a dynamic time of healing and growth for organisms. For example, during stages 3 and 4, or slow wave sleep, growth hormone levels increase, and changes in immune function occur. The myriad illnesses associated with sleep deprivation testify to its restorative function.
According to the Ontogenetic Hypothesis of REM sleep, the activity occurring during neonatal REM sleep (or Active Sleep) seems to be particularly important to the developing organism (Marks et al., 1995). Studies investigating the effects of Active Sleep deprivation have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass (Mirmiran et al. 1983), and an abnormal amount of neuronal cell death (Morrissey, Duntley & Anch, 2004). Given sleep's heterogeneous nature, however, no single theory predominates as it is difficult to describe one single "function" of sleep.
One process known to be highly dependent on sleep is memory. REM sleep appears to help with the consolidation of spatial and procedural memory, while Slow-wave sleep helps with the consolidation of declarative memories. When experimental subjects are given academic material to learn, especially if it involves organized, systematic thought, their retention is markedly increased after a night's sleep. Mere rote memorization is retained similarly well without an intervening period of sleep.
Non-REM sleep is an anabolic state marked by physiological processes of growth and rejuvenation of the organism's immune, nervous, muscular, and skeletal systems. Sleep also restores neurons and increases production of brain proteins and certain hormones. Wakefulness may perhaps be viewed as a cyclical, temporary, hyperactive catabolic state during which the organism acquires nourishment and procreates. Asking the question "Why do we awaken?" instead of "Why do we sleep?" yields a different perspective toward understanding how sleep and its stages contribute to a healthy organism.
posted by loseword @ 11:21 PM
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