Toddlers (age 1 to 3) and children (age 3 to 9)Īround the ages of two to five, the total sleep time needed each day decreases by two hours, from 13 to 11 hours. At 12 months of age, infants typically sleep 14-15 hours per day, with most sleep now occurring in the evening with only one to two naps needed during the day. At six months of age, the longest continuous sleep episode lengthens to six hours. The total NREM and REM sleep cycle is typically 50 minutes instead of the adult 90-minute cycle. At this time, REM sleep decreases and shifts to the later part of the sleep cycle. Three months of age is when the cycling of melatonin and cortisol in a circadian rhythm occurs and when sleep onset begins with NREM. At two months of age, the progression of nocturnal sleeping begins. These differences in sleep and sleep stages occur as circadian rhythms have not fully been determined.Ĭircadian rhythms begin to develop around two to three months of age, with greater durations of waking hours during the day and longer periods of sleep at night. In contrast to children and adults, newborn sleep onset occurs through REM, not NREM, with each sleep episode consisting of only one or two cycles. Newborns have three different types of sleep: quiet sleep (similar to NREM), active sleep (similar to REM), and indeterminate sleep. Newborns sleep approximately 16-18 hours per day discontinuously, with the longest continuous sleep episode typically lasting 2.5 to 4 hours. Sleep timing in newborns is distributed evenly across day and night for the first few weeks of life, with no regular rhythm or concentration of sleeping and waking. The time spent in each sleep stage develops and changes as we age, with the consistent trend being that amounts of sleep decrease as individuals age. HA is released from histamine-containing neurons of the tuberomammillary nucleus of the posterior thalamus. The cell bodies of hypocretin-producing neurons are localized to the dorsolateral hypothalamus and send projections to all the major brain regions that regulate arousal. The noradrenergic cells of the LC inhibit REM sleep, promote wakefulness, and project to various other arousal-regulating brain regions, including the thalamus, hypothalamus, basal forebrain, and cortex. NE is released from norepinephrine-containing neurons of the locus coeruleus (LC). 5-HT is released from serotonin-containing neurons of the dorsal raphe nucleus. Cortical ACh release is greatest during waking and REM sleep and lowest during NREM sleep. Neurochemicals such as acetylcholine (ACh), dopamine (DA), norepinephrine (NE), serotonin (5-HT), histamine (HA), and the peptide hypocretin maintain the waking state. Adenosine also promotes sleep by inhibiting wakefulness-promoting neurons localized to the basal forebrain, lateral hypothalamus, and tuberomammillary nucleus. Sleep-promoting neurons in the anterior hypothalamus release GABA, which inhibits wake-promoting regions in the hypothalamus and brainstem. GABA is the primary inhibitory neurotransmitter of the central nervous system (CNS), and it has been well established that activation of GABA-a receptors favors sleep.
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