Chapter 8: Rythms Waking and Sleeping

Question 1

endogenous circadian

rhythms 262

Answer 1

Evidently, birds generate a rhythm that prepares them for seasonal changes. We refer to that rhythm as an endogenous circannual rhythm.

Question 2

endogenous circannual

rhythm 262

Answer 2

Controls the time of: waking, sleeping, eating, metabolism, mood.

Question 3

zeitgeber 264

Answer 3

The stimulus that resets the circadian rhythm is
referred to by the German term zeitgeber meaning “time-giver.” Light is the dominant zeitgeber for land
animals. In addition to light, other zeitgebers include exercise, arousal of any kind meals, and the temperature of the environment. Social stimuli—that is, the effects of other people—are ineffective as
zeitgebers, unless they induce exercise or other vigorous activity. Although these additional zeitgebers modify the effects of light, they have only weak effects on their own.

Question 4

jet lag 265

Answer 4

disruption of circadian rhythms due to crossing time zones is known as jet lag. Travelers complain of sleepiness during the day, sleeplessness at night, depression, and impaired concentration. All 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 adjusted to the new schedule. We phase-delay our circadian
rhythms. Going east, we phase-advance to sleep earlier
and awaken earlier.

Question 5

suprachiasmatic nucleus

(SCN) 267

Answer 5

Although cells throughout the body generate circadian
rhythms, the main driver of rhythms for sleep and body temperature is the suprachiasmatic nucleus, or SCN, a part of the hypothalamus. It gets its name from its location just above (“supra”) the optic chiasm. After damage to the SCN, the body’s rhythms become erratic. A small branch of the optic nerve, known as the retinohypothalamic path, from the retina to the SCN, alters the SCN’s settings.

Question 6

melatonin 269

Answer 6

The pineal gland releases the hormone
melatonin, which influences both circadian and circannual rhythms. The pineal gland secretes melatonin mostly at night, making us sleepy at that time. When people shift to a new time zone and start following a new schedule, they continue to feel sleepy at their old times until the melatonin rhythm shifts. People who have pineal gland tumors sometimes stay awake for days at a time. Melatonin secretion starts to increase about 2 or 3 hours before bedtime. Taking a melatonin pill in the evening has little effect on sleepiness because the pineal gland produces melatonin at that time anyway. However, people who take melatonin earlier start to become sleepy. In the process, it shifts the circadian rhythm such that the person starts to become sleepy earlier than usual the next day also.

Question 7

pineal gland 269

Answer 7

The SCN regulates waking and sleeping by controlling activity levels in other brain areas, including the pineal gland, an endocrine gland located just posterior
to the thalamus.