18. Sleep II Flashcards
(25 cards)
What are circadian rhythms?
Internal timekeeping systems that align with the Earth’s 24-hour cycle
They evolved as an adaptation to the daily light-dark cycle.
What is the significance of circadian rhythms?
They contribute significantly to health and wellbeing by optimizing tissue function for appropriate times of day
What are other types of natural rhythms besides circadian rhythms?
- Yearly (seasonal) rhythms
- Monthly (lunar) rhythms
- Tidal rhythms
What is the master clock of the body?
The suprachiasmatic nucleus (SCN) in the hypothalamus
Where is the suprachiasmatic nucleus (SCN) located?
Just above where optic nerves cross
What type of cells provide light information to the SCN?
Intrinsically photosensitive retinal ganglion cells
What unique features does the brain clock have?
- Direct light input
- Interconnected circuits for robust timekeeping
- Synchronizes peripheral clocks throughout the body
What mechanisms synchronize peripheral clocks?
- Body temperature rhythms (1-1.5° fluctuation daily)
- Hormonal signals
- Direct innervation from the central nervous system
- Food intake rhythms
What does chronomedicine recognize?
Body function varies predictably throughout the day
What are examples of daily rhythms in body functions?
- Blood pressure
- Medication metabolism
What are health consequences of disrupting circadian rhythms?
- Increased risk for cancer
- Diabetes
- Obesity
- Stroke
- Heart disease
- Depression
- Cognitive impairment and accidents
What key discoveries were made about circadian rhythms in Drosophila?
- Control overt rhythms
- Can be entrained to environmental cues
- Maintain autonomous rhythms in constant conditions
- Temperature compensation
What is the molecular clock mechanism based on?
A delayed negative feedback loop of gene expression
What are the transcriptional activators involved in the molecular clock of Drosophila?
- CLOCK
- CYCLE
What role does DOUBLE-TIME kinase play in the molecular clock?
Regulates PERIOD by phosphorylating it, targeting it for degradation
What is the function of TIMELESS in the molecular clock mechanism?
Protects PERIOD from degradation
What happens after PERIOD and TIMELESS accumulate in the cytoplasm?
The PERIOD-TIMELESS complex enters the nucleus and inhibits CLOCK-CYCLE activity
What is the effect of light at different times on circadian rhythms?
- Early night light delays the clock (interpreted as late dusk)
- Late night light advances the clock (interpreted as early dawn)
What photoreceptor is involved in light detection in Drosophila?
CRYPTOCHROME
How does CRYPTOCHROME interact with TIMELESS?
Binds to TIMELESS in the presence of blue light, leading to TIMELESS degradation
What are the similarities between mammalian and Drosophila clocks?
Uses similar molecular mechanisms but with different components
How are PERIOD proteins regulated in mammals?
By CRY rather than TIMELESS
What is the role of specialized clock neurons?
Communicate via neuropeptides to control sleep-wake cycles
What is PDF in Drosophila equivalent to in mammals?
VIP in mammalian SCN
