Brain chemical cycles cause awakeness and sleep {sleep, state}. Sleep can be unconscious or have dreaming.
causes
Monotony, warmth, and restricted movement make people sleepy. Waiting for something that cannot happen yet can make people sleepy. Regular physical exercise, good-quality firm mattress, warm but ventilated room, malted milk drink, and sexual satisfaction at bedtime promote good sleep. Deep sleep can follow epilepsy.
causes: biology
Melatonin induces sleep at night {sleep inducer} and maximizes just before morning. Neurosteroid induces sleep, can be analgesic at high concentration, and comes from cholesterol or progesterone. Sleep peptide is in brain, cerebrospinal fluid, and cerebral blood and can induce sleep.
Brain stops making monoamine neurotransmitters. Monoamine oxidase breaks down monoamines. Monoamines no longer excite motor neurons, and acetylcholines excite motor neurons. However, monoamines still go to eye-muscle nerves. When asleep, amygdala inhibits pons, which activates medial medulla, which inhibits motor neurons.
awake
When awake, forebrain inhibits amygdala, which excites pons, which inhibits locus coeruleus, which excites muscles. Monoamines block sleep by exciting motor neurons. At awakening, acetylcholine is low, and serotonin and norepinephrine are high.
brain
Arousal system, hypothalamus, locus coeruleus, raphé nuclei, and reticular nucleus affect sleep. During NREM sleep, thalamus-cortex pathways have inhibition. During REM sleep, thalamus-cortex pathways have no inhibition but receive only small input.
Pons reticular activating system has norepinephrine, serotonin, dopamine, and acetylcholine secreting neurons and has pathways to brainstem neurons. Reticular activating system neurons can inhibit afferent axons from senses and efferent axons to muscles.
animals
Higher invertebrates and chordates have rest phases. Sleep is only in vertebrates. Fish and amphibia sleep briefly or just rest. Ancient reptiles have only NREM sleep. Recent reptiles and birds have NREM sleep and some REM sleep. Mammals have NREM sleep and more REM sleep. Mammals who are more immature at birth have more REM sleep. For mammals, REM sleep is at highest percentage at birth and decreases with age. Larger mammals sleep more. In dolphins, one hemisphere NREM-sleeps for several hours, then other hemisphere NREM-sleeps, so they can continue to breathe.
Sleep is an instinct. Sleep evolved separately from dreams [Horne, 1988].
amount
In all species, sleep amount is directly proportional to waking metabolic rate. Animals with higher body temperatures, shorter reaction times, and more fat sleep longer. Birds and mammals that are not secure from predators sleep only for minutes at a time. Predators, who can sleep safely, sleep longer.
Newborns sleep 80%, with seven or eight naps per day. 12-to-18-month-old toddlers sleep 50%. Three-year-old children sleep 40%, and REM sleep is 20% of sleep. Teenagers and adults sleep 30%. Older adults have shorter and more broken sleep.
In adults, sleep amount is proportional to body weight.
purposes
Sleep causes more protein synthesis and less cellular work and so aids growth. Perhaps, sleep simplifies brain processes by removing alternative pathways. Perhaps, simple brain-activity patterns repeat and return neurons to sense and motor readiness.
Consciousness>Consciousness>States>Sleep
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Date Modified: 2022.0224