The onset of sleep is associated with a variety of changes in both behavioral and
physiologic states. Sleep is not a uniform state either: it has different stages that affect
different areas of the brain and body. Nonrapid eye movement sleep stages are as different
from rapid eye movement sleep as is wakefulness. Circadian rhythms of physiologic systems
also impact wake, sleep, sleepiness, and alertness. There are characteristic changes in both
sleep patterns and circadian rhythm that occur with aging. The cardiovascular, respiratory …