Environmental Influences Flashcards
What are the three characteristics that define circadian rhythms?
- Self sustaining with tau ~24 hours in constant conditions
- Temperature compensated
- Entrainable to one or more periodic stimuli in the environment
Oscillators
Devices that produce a rhythm
Pacemakers
“Master” oscillators that control the timing of other oscillators and many rhythms
Slave or secondary oscillators
Typically control only one rhythm or rhythms of local functions
Would removal of a slave oscillator disrupt all other rhythms?
No
Clocks
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
Interval timer
A type of clock, but one that can only time one cycle, at which point it stops unless it is reset
What are the two problems presented by the fact that the circadian clock has a period that is not exactly 24 hours?
- 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?
Negative masking
Suppressing a behaviour that would normally be present at that time of day
Positive masking
Stimulating a behaviour that would normally be absent at that time of day
What kind of rhythm is shown in IMAGE 4?
An entrained rhythm
What kind of rhythm is shown in IMAGE 5?
A masked rhythm
What does IMAGE 6 show?
A phase delay
In a phase-response curve, what is the X axis?
The circadian phase at which the drug or other stimulus is administered
What is a circadian hour?
1/24th of a full circadian cycle
If the free-running circadian period is 25 hours, what would a circadian hour be equal to?
Slightly more than one real hour, it would be equal to 25/24
Why do we use circadian hours?
Because then we can compare between animals that have circadian rhythms slightly different than humans
What is the designated circadian time for the beginning of subjective night?
CT12
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?
CT0
What is the hypothesis of the nonparametric entrainment model?
Entrainment is achieved by a daily adjustment of rhythm phase, to offset the difference between Tau and 24 hour T
What is the evidence to support the nonparametric entrainment model?
- 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
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?
- 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)
Early in the subjective night, light induces what kind of shift?
Phase delay
Late in the subjective night, light induces what kind of shift?
Phase advance
