Sleep Disorders and Sleep Deprivation An Unmet Public Health Problem (2006) / Chapter Skim
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2 Sleep Physiology
2 Sleep Physiology
Pages 33-54
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From page 33... ...
sleep. NREM sleep is divided into stages 1, 2, 3, and 4, representing a continuum of relative depth.
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From page 34... ...
This chapter provides an overview of basic sleep physiology and describes the characteristics of REM and NREM sleep. Sleep and circadian-generating systems are also reviewed.
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From page 35... ...
As the sleep episode progresses, stage 2 begins to account for the majority of NREM sleep, and stages 3 and 4 may sometimes altogether disappear. Four Stages of NREM Sleep The four stages of NREM sleep are each associated with distinct brain activity and physiology.
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From page 36... ...
. Stages 3 and 4, Slow-Wave Sleep Sleep stages 3 and 4 are collectively referred to as slow-wave sleep (SWS)
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From page 37... ...
. TABLE 2-1 Physiological Changes During NREM and REM Sleep Physiological Process NREM REM Brain activity Decreases from wakefulness Increases in motor and sensory areas, while other areas are similar to NREM Heart rate Slows from wakefulness Increases and varies compared to NREM Blood pressure Decreases from wakefulness Increases (up to 30 percent)
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From page 38... ...
. · Sympathetic-nerve activity: Sympathetic-nerve activity decreases as NREM sleep deepens; however, there is a burst of sympathetic-nerve activity during NREM sleep due to the brief increase in blood pressure and heart rate that follows K-complexes.
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From page 39... ...
. · Cerebral blood flow: NREM sleep is associated with significant reductions in blood flow and metabolism, while total blood flow and metabolism in REM sleep is comparable to wakefulness (Madsen et al., 1991b)
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From page 40... ...
These neurons send outputs to the lower brainstem and spinal cord that cause muscle atonia, REMs, and chaotic autonomic activity that characterize REM sleep. Other outputs are sent to the forebrain, including activation of the cholinergic pathways to the thalamus to activate the EEG.
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From page 41... ...
They control the sleep-wake cycle, modulate physical activity and food consumption, and over the course of the day regulate body temperature, heart rate, muscle tone, and hormone secretion. The rhythms are generated by neural structures in the hypothalamus that function as a biological clock (Dunlap et al., 2004)
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The Suprachiasmatic Nucleus The suprachiasmatic nucleus (SCN) is responsible for regulating circadian rhythms in all organs.
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, and an increase in heat loss, all which promote sleep onset and maintenance, as well as EEG slow-wave activity. Conversely, there is a gradual increase in body temperature several hours before waking.
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. Sleep onset occurs through REM, not NREM, and each sleep episode consists of only one or two cycles (Jenni and Carskadon, 2000; Davis et al., 2004)
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. By 3 months of age, sleep cycles become more regular: sleep onset now begins with NREM, REM sleep decreases and shifts to the later part of the sleep cycle, and the total NREM and REM sleep cycle is typically 50 minutes (Anders et al., 1995; Jenni and Carskadon, 2000)
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From page 46... ...
. One study found that children appear to have longer REM sleep latencies than adolescents and consequently spend a greater percentage of sleep time in stages 3 and 4 (Gaudreau et al., 2001)
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Arousal occurring mostly from REM sleep in young adults suggests that there is a protective mechanism to keep from awakening during NREM sleep; however, this protective effect appears to also decline with age (Dijk, 1998)
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. Another gender contrast is that older women go to bed and wake up earlier than older men, which suggests that body temperature rhythms are phase-advanced in elderly women (Campbell et al., 1989;
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From page 49... ...
In: Lee-Chiong TL, Sateia MJ, Carskadon MA, eds. Sleep Medicine.
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From page 50... ...
In: Kryger MH, Roth TT, Dement WC, eds. Principles and Practice of Sleep Medicine.
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2001. Age-related modifications of NREM sleep EEG: From childhood to middle age.
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1993. Heart rate and blood pressure consequences of an afternoon SIESTA (Snooze-Induced Excita tion of Sympathetic Triggered Activity)
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From page 53... ...
In: Kryger MH, Roth T, Dement WC, eds. Principles and Practice of Sleep Medicine.
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