Module 8.1

What is the principal zeitgeber for land animals?​

light

A small branch of the optic nerve, known as the ____ path extends directly from the retina to the SCN.​

retinohypothalamic

The proteins PER and TIM, originally discovered in insect but now found in mammals also, influence circadian rhythms by ____.​

building up during the day and declining during sleep

​A disruption of circadian rhythms due to crossing time zones is known as ____.

jetlag

An astronaut orbiting earth experiences 45-minute periods of daylight alternating with 45-minutes periods of darkness. What is likely to happen? ​

​They sleep poorly during rest periods.

​Suppose you fell into a cave and lost your watch. Without any time cues, your circadian rhythm would ____.

​remain relatively stable

The suprachiasmatic nucleus is found in the ____. ​

​hypothalamus

What happens after damage to the suprachiasmatic nucleus itself?​

​Animals' activity patterns become less consistent and no longer respond to light and dark cycles.

Which of the following is most clearly under the control of a circadian rhythm in most animals?​

sleep

Social stimuli - that is, the effects of other people - are weak ____, unless they induce exercise or other vigorous activity.​

zeitgebers

A person's circadian activity cycle would most likely drift out of phase with the activity of other people if the person ____.​

​spends a period of time in seclusion, away from sunlight

A "zeitgeber" is a(n) ____.​

environmental cue that resets a biological clock

The SCN produces circadian rhythms by altering ____.​

​production of proteins

Researchers have demonstrated that the expression of the SCN genes can be changed through ____.​

exposure of the eyes to light

​The SCN is located just above the ____.

optic chiasm

The circadian rhythm is reset by input from special ganglion cells in the retina. These ganglion cells are unusual in that they ____.​

​respond directly to light, but respond very slowly

A human's body temperature over the course of 24 hours is usually highest ____.​

mid to late afternoon

Mammals have circadian rhythms ____.​

for a variety of activities, including sleep

What is the role of the suprachiasmatic nucleus in circadian rhythms?​

​Its neurons generate a 24-hour rhythm by themselves.

When do the secretions of melatonin begin?​

​a couple of hours before a person naturally falls asleep

Animals produce endogenous circadian rhythms that last ____.​

about a day

If suprachiasmatic nucleus neurons are disconnected from the rest of the brain, they ____.​

continue to produce activity that follows a circadian rhythm

The pineal gland releases the ____ hormone, which influences both circadian and circannual rhythms. ​

​melatonin

Research on circadian rhythms has shown that one of the best ways to increase the alertness and efficiency of workers on night shifts is to ____.​

​expose them to bright lights while they work

Suppose you work on a submarine with only artificial light. You are required to follow a schedule of working for 12 hours and then sleeping for 6. What rhythm, if any, will your alertness and body temperature show?​

They will follow the usual rhythm of 24 hours.

Based on research, it has been determined that the human circadian rhythm appears to be ____.​

​just over 24 hours

What does "endogenous" mean?​

generated from within

Which statement is TRUE with regard to the duration of a self-generated sleep/activity cycle?​

It is highly consistent in a given individual in a given environment.

When traveling across time zones, how does the direction of travel affect one's adjustment to the new time zone?​

Travel to the west is easier.