Environmental Influences

Question 1

What are the three characteristics that define circadian rhythms?

Answer 1

• Self sustaining with tau ~24 hours in constant conditions
• Temperature compensated
• Entrainable to one or more periodic stimuli in the environment

Question 2

Oscillators

Answer 2

Devices that produce a rhythm

Question 3

Pacemakers

Answer 3

“Master” oscillators that control the timing of other oscillators and many rhythms

Question 4

Slave or secondary oscillators

Answer 4

Typically control only one rhythm or rhythms of local functions

Question 5

Would removal of a slave oscillator disrupt all other rhythms?

Answer 5

No

Question 6

Clocks

Answer 6

Oscillators that are linked to the external world, so that the phase of the oscillator corresponds to a time of day in the outside world

Question 7

Interval timer

Answer 7

A type of clock, but one that can only time one cycle, at which point it stops unless it is reset

Question 8

What are the two problems presented by the fact that the circadian clock has a period that is not exactly 24 hours?

Answer 8

• How is tau made equivalent to the period of the light/dark cycle?
• How is the timing of the circadian cycle controlled, so that nocturnal animals are active and night and not in the day?

Question 9

Negative masking

Answer 9

Suppressing a behaviour that would normally be present at that time of day

Question 10

Positive masking

Answer 10

Stimulating a behaviour that would normally be absent at that time of day

Question 11

What kind of rhythm is shown in IMAGE 4?

Answer 11

An entrained rhythm

Question 12

What kind of rhythm is shown in IMAGE 5?

Answer 12

A masked rhythm

Question 13

What does IMAGE 6 show?

Answer 13

A phase delay

Question 14

In a phase-response curve, what is the X axis?

Answer 14

The circadian phase at which the drug or other stimulus is administered

Question 15

What is a circadian hour?

Answer 15

1/24th of a full circadian cycle

Question 16

If the free-running circadian period is 25 hours, what would a circadian hour be equal to?

Answer 16

Slightly more than one real hour, it would be equal to 25/24

Question 17

Why do we use circadian hours?

Answer 17

Because then we can compare between animals that have circadian rhythms slightly different than humans

Question 18

What is the designated circadian time for the beginning of subjective night?

Answer 18

CT12

Question 19

If the organism had a perfectly symmetrical circadian rest-activity cycle (12 hours rest and 12 hour activity), what would the designated circadian time for the beginning of subjective day be?

Answer 19

CT0

Question 20

What is the hypothesis of the nonparametric entrainment model?

Answer 20

Entrainment is achieved by a daily adjustment of rhythm phase, to offset the difference between Tau and 24 hour T

Question 21

What is the evidence to support the nonparametric entrainment model?

Answer 21

• Flying squirrels were kept in a dark nest and had to emerge for food and water
• If the lights were on when they emerged, they would go back and wait 15 minutes before re-emerging
• This small phase delay every few days was sufficient for entrainment

Question 22

According to the nonparametric entrainment model, if you know the shape of the PRC and the period, you can predict what important properties of entrainment to LD cycles?

Answer 22

• Limits to entrainment (circadian rhythms will entrain only to LD cycles that have a period relatively close to 24 hours)
• Phase of entrainment (the period of the clock should determine the timing of circadian rhythms when they are stably entrained)
• Gradual re-entrainment (when a LD cycle is shifted, the circadian clock should re-entrain gradually over several days rather than instantly, because there is a maximal amount that the clock can be shifted each day)

Question 23

Early in the subjective night, light induces what kind of shift?

Answer 23

Phase delay

Question 24

Late in the subjective night, light induces what kind of shift?

Answer 24

Phase advance

Question 25

What are the 3 regions of a PRC?

Answer 25

• Unresponsive zone in the subjective day
• A phase delay zone in the early part of the subjective night
• A phase advance zone in the late part of the subjective night

Question 26

The basic PRC shape is characteristic of what organisms?

Answer 26

All organisms that can be entrained by light

Question 27

A longer tau would result in what?

Answer 27

Late rising

Question 28

A shorter tau would result in what?

Answer 28

Early rising

Question 29

What are two circadian clock properties?

Answer 29

• Rate of cycling

- Circadian rhythm of sensitivity to light

Question 30

People can adjust to time differences by how many hours per day?

Answer 30

1-2 hours

Question 31

What are the factors that determine how long it takes to shift to a new time zone?

Answer 31

• Magnitude of shift
• Direction of shift
• Timing of light exposure
• Parameters of light stimulus