Flashcards in Final exam Deck (31):
In the presence of an appropriate environmental stimulus, circadian rhythms exhibit what?
Stable phase relations relative to local time and to each other
What happens to circadian rhythms in the absence of entraining stimuli?
They free run with a species-typic circadian period
Free-running indicates what?
Control by one or more endogenous, self-sustaining circadian oscillators
Humans maintained in constant conditions, or with self-control of environmental light but no knowledge of clock time, exhibit what?
Free-running circadian rhythms with t in the 24-25 hour range
Describe the sleep-wake cycle in humans under constant conditions
Initially assumes a delayed phase relative to the body temperature cycle (sleep onset closer to the body temperature minimum)
What happens to sleep-wake cycles if temporal isolation is maintained for a month or more?
Most individuals exhibit a spontaneous uncoupling of sleep-wake cycle and body temperature cycles (spontaneous internal desynchronization)
The fact that different sets of rhythms can become uncoupled and free-run with different circadian periods suggests what?
That there may be two circadian pacemakers; a strong oscillator in core body temperature and a weak oscillator in sleep-wake
Explain the Andech studies challenge to the two-pacemaker model
When naps were included in the analysis, sleep episodes were found to occur at most or all body temperature minimums (no desynchrony there)
The circadian rest-activity rhythm divides into two components, one of which slows while the other accelerates, until stable coupling is achieved in anti phase, creating the appearance of a 12h free-running rhythm
In nocturnal rodents, constant bright light can induce what?
The circadian clock system must contain what 3 elements?
- An input from the environment
- An oscillator that generates a rhythm
- Outputs from the oscillator that drive rhythms in other brain systems
Explain complex phenomena at the simplest level possible
Properties of rhythms; the things we want to explain at the neuronal level
What are the two possibilities for what's in the "black box"?
- Individual neurons in the SCN might all be circadian oscillators
- Neurons in the SCN might be wired in a way that produces a daily rhythm, even if individual neurons cannot oscillate with a circadian periodicity on their own
The primary negative feedback loop involves what proteins?
PER and TIM
When does TIM normally rise and peak?
Rises at nighttime, peaks in the middle of the night
Degrading TIM early in the night does what?
Moves the TIM cycle back in time (delays its progression(
Degrading TIM late in the night does what?
Moves TIM forward in time (advances its progression)
When does per gene activity normally increase?
Late in the night
What things can happen if coupling is disrupted?
- Loss of rhythms (in bright light)
- Damping of rhythms with aging
- Splitting of rhythms (in bright light)
- Delayed shifting of rhythms
Rods are typically associated with what?
Vision in dim light
Cones are typically associated with what?
Colour vision in bright light
The master clock in mammals (the SCN) receives its retinal projections from where?
The retinohypothalamic tract
What is the retinohypothalamic tract formed from?
A small number of distinct ganglion cells
What is the role of glutamate in retinal projections to the SCN?
Glutamate carries the light info signal to individual SCN neurons
In mammals, what happens if the eyes are lost?
They are then visually and circadian blind and they will be unable to entrain to light and will free-run
In fish, birds, reptiles, and amphibians, what happens if the eyes are removed and why?
They can still maintain an entrained circadian rhythm because they have several light-sensing extra-ocular photoreceptor organs other than the eyes
Describe the retinal degeneration mutant mouse
Despite the near-complete loss of their rods and cones, they still had apparently normal circadian responses to light
What are the two SCN input pathways that have been implicated in non-photic circadian clock resetting?
- The geniculohypothalamic tract (GHT) originating in the intergeniculate leaflet (IGL)
- An ascending serotonergic pathway originating in the pontine raphe nuclei
Where does the geniculohypothalamic tract (GHT) originate?
In the intergeniculate leaflet (IGL)