Your body spontaneously generates its own rhythm of ____ and ____.
wakefulness and sleep
Research as early as that of _________ implied that the body generates its own cycles of activity and inactivity.
Curt Richter (1922)
Evidently, the bird generates a rhythm that prepares it for seasonal changes. We refer to that rhythm as an ____ ____ ____.
endogenous circannual rhythm
Animals also produce ____ ____ ____ that last about a day.
endogenous circadian rhythms
The light from the sun helps you feel less sleepy, but also your urge to sleep depends partly on the ________, not just how long you have been awake.
time of day
Humans also generate wake-sleep rhythms, and we find it difficult to sleep on anything far from a ________.
____ ____ affect much more than just waking and sleeping. We have circadian rhythms in our eating and drinking, urination, secretion of hormones, sensitivity to drugs, and other variables.
We also have circadian rhythms in ____. In one study, young adults recorded their mood every two hours throughout the day. Most showed increases in positive mood (happiness) from waking until late afternoon, and then a slight decline from then to bedtime.
Circadian rhythms differ among individuals. Some people (____ ____, or larks) awaken early, quickly become productive, and become less alert as the day progresses. Others (____ ____, or owls) warm up slowly, reaching their peak in the late afternoon or evening.
morning people : evening people
As a child, you went to bed early and woke up early. As an adolescent you started staying up later and waking up later, when you had the opportunity. The mean preferred time of going to sleep gets later and later until about age 20 and then starts a ____ ____.
Our circadian rhythms generate a period close to ______, but they are not perfect. We readjust our internal workings daily to stay in phase with the world.
Although circadian rhythms persist without light, light is critical for ____ ____. Without something to reset your circadian rhythm, it would gradually drift away from the correct time.
The stimulus that resets the circadian rhythm is referred to by the German term ____, meaning "time-giver". Light is the dominant ____ for land animals.
In addition to light, other zeitgebers include____, ____ of any kind, ____, and the ____ of the environment.
exercise, arousal, meals, temperature
Social stimuli - that is, the effects of other people - are ____ zeitgebers, unless they induce exercise of other vigorous activity.
These additional zeitgebers merely ____ or alter the effects of light. On their own, their effects are weak.
Even when we try to set our wake-sleep cycles by the clock, ____ has its influence. Consider what happens when we shift to daylight savings time in spring.
A disruption of circadian rhythms due to crossing time zones is known as ___ ___.
Travelers complain of sleepiness during the day, sleeplessness at night, depression, and impaired concentration. All of these problems stem from the mismatch between ___________.
internal circadian clock and external time
Most people find it easier to adjust to crossing time zones going _________.
west than east
Going west, we stay awake later at night and then awaken late the next morning, already partly adjust to the new schedule. We _____ our circadian rhythms.
Going east, we _______ to sleep earlier and awaken earlier. Most people find it difficult to go to sleep before their body's usual time and difficult to wake up early the next day.
Adjusting to jet lag is often stressful. Stress elevates blood levels of the adrenal hormone ____, and many studies have that prolonged elevations of ____ damage neurons in the hippocampus, a brain area important for memory.
Shift work. People who sleep irregularly - such as pilot, medical interns, and shift workers in factories - find that their ____ of sleep depends on when they go to sleep. When that have to sleep in the morning or early afternoon, they sleep only briefly, even if they have been awake for many hours.
Even after months or years on such a schedule, many workers adjust ____. They continue to feel groggy on the job, they sleep poorly during the day, and their body temperature continues to peak when they are sleeping during the day instead of while they are at work during the night.
People adjust best to night work if they sleep in a ____ ____ room during the day and work under ____ ____ lights at night, comparable to noon day sun.
very dark : very bright