When sleeping, people go through four non-REM-sleep stages {sleep cycle}, separated by short REM-sleep periods. Sleep cycles last 90 minutes and have short dreaming stage 1, then stage 2, then stage 3, then stage 4, then stage 3, then stage 2, then dreaming stage 1, and then waking. In stage 1, heart rate and respiration rate increase, and brain is active [Dement, 1972]. Sleep gets deeper through the night. Deep sleep is greatest at 2 AM.
Awake/NREM-sleep/REM-sleep cycle has different properties at each stage {AIM model}. Sleep-cycle stages have different Activation levels, Input and output, and neurotransmitter Modulation.
activation
Activation is from pons reticular activating system and has pathways to nearby brainstem areas, thalamus, and spinal cord. Awakeness and REM sleep have high-frequency low-amplitude EEG waves. NREM sleep has low-frequency high-amplitude EEG waves. Stage II NREM sleep has distinctive sleep-spindle EEG.
Cortical regions differ in activation cycles, input, output, and modulation. Hypothalamus superchiasmatic nucleus starts NREM sleep and controls progress through NREM sleep. REM sleep activation goes from pons to lateral geniculate to occipital (PGO). Reticular formation blocks spinal-cord sense and motor activity during REM sleep [Hobson, 1989] [Hobson, 1994] [Hobson, 1999] [Hobson, 1999] [Hobson, 2002] [Hobson et al., 1998].
input and output
Reticular activating system neurons can inhibit afferent axons from senses and efferent axons to muscles. For awakeness, input comes from outside, and output goes to muscles. For NREM and REM sleep, inputs only come from inside, with no muscle output.
modulation
Modulation is by norepinephrine, serotonin, dopamine, and acetylcholine secretions from pons reticular-activating-system neuron axons. Awakeness has high norepinephrine, serotonin, and dopamine and low acetylcholine. REM sleep has low norepinephrine and low serotonin but moderate dopamine and high acetylcholine. NREM sleep has neither high nor low neurotransmitter levels.
Cholinergic axons go to amygdala and multisensory posterolateral cortex and fire when eyes move.
cycles
Sleep has four or five cycles. First cycle has long deep NREM sleep and short REM sleep. Last cycle has long REM sleep and short shallow NREM sleep.
Regular sleep {orthodox sleep} {non-rapid eye movement sleep}| {NREM sleep} {light sleep} has only small eye movements.
properties
Consciousness is not present in slow-wave sleep. NREM sleep has little dreaming but seems to have "thinking". Both REM and non-REM sleep can have talking. Words relate to thoughts or dreams.
amount
NREM sleep is 80% of human sleep.
animals
Only vertebrates have NREM sleep. Ancient reptiles have some NREM sleep. Recent reptiles and birds have NREM sleep and little REM sleep. Mammals have NREM sleep and REM sleep.
In dolphins, one hemisphere NREM-sleeps for several hours, then other hemisphere NREM-sleeps, so they can always breathe.
causes
Melatonin, which brain makes more at night, promotes NREM sleep. During NREM sleep, acetylcholine changes from low to high. During NREM sleep, serotonin and norepinephrine change from high to low.
NREM sleep releases growth hormone, decreases adrenaline and corticosteroids levels, and increases cortisol and testosterone.
Raphe-system serotonin acts on thalamus layer-five and layer-six neurons to start light sleep.
Serotonin constricts pupils.
biology
NREM sleep has low frontal cortex activity, low cortical activity, high limbic activity, and high forebrain sleep-on-cell activity.
In NREM sleep, nerve cells synchronize at low frequency.
Hypothalamus superchiasmatic nucleus starts NREM sleep and controls progress through NREM sleep.
purposes
Perhaps, non-REM sleep reduces free-radical damage.
Sleep {paradoxical sleep} {rapid eye movement sleep}| {REM sleep} {deep sleep} can have dreaming.
properties
REM sleep has limited consciousness. REM sleep has detailed dreams. Both REM and non-REM sleep can have talking. Words relate to thoughts or dreams. REM sleep completely relaxes most body muscles and stops many reflexes but has rapid eye movements. In men, REM sleep has penis erections. During REM sleep, mammals have no temperature control.
amount
Paradoxical sleep is 20% of sleep.
20-week-old fetuses have REM sleep, indicating dreaming. For mammals, REM sleep is at highest percentage at birth and decreases with age. Three-year-old children and adults sleep 20% in REM sleep.
REM sleep diminishes with anxiety.
Recent reptiles and birds have NREM sleep and little REM sleep. Mammals have NREM sleep and REM sleep. Mammals who are more immature at birth have more REM sleep.
causes
REM sleep has high acetylcholine, from brainstem, but low serotonin and norepinephrine, from sense input.
REM sleep diminishes with adenosine, barbiturate, benzodiazepines, depressants, interleukin, and sedatives.
biology
REM sleep has high limbic activity, low cortex input and output, no sense input, and no motor neuron output. REM sleep-on cells are highly active. REM sleep has faster brain blood flow than wakeful rest.
Awakening sense thresholds are highest in REM sleep, except for stage-4 sleep.
REM sleep activation goes from pons to lateral geniculate to occipital lobe (PGO).
factors
Men and women have same REM-sleep activation system and REM sleep amounts. In mental defectives, REM sleep percentage is proportional to intelligence level.
purposes
Perhaps, REM sleep is for monoamine decrease. REM sleep is probably not for readiness or memory consolidation.
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Date Modified: 2022.0225