Circadian Rhythm Flashcards
What does the utility of circadian rhythms rely on?
Proper timing relative to stochastic external environmental cycles
What does this mean for the construction of circadian rhythms?
Entrainment to external time cues or zeitgeber.
What is the principle zeitgeber for mammals?
Light.
What are Phase Response Curves?
These allow studying of effects of external stimuli on endogenous rhythms, by characterising phase shift induced by stimulus application at different phases of an oscillation.
Where is the mammalian circadian rhyhtm found?
Hypothalamus superchiasmatic nucleus.
What is the general micro structure of the SCN
Thousands of coupled clock neurons containing biochemical oscillators.
How does a light stimulus relate to the structure of SCN?
Shifts oscillations of individual clock neurons, that in turn shift collective rhythm produced by the ensemble.
What is the biological basis of how the CR interprets light?
Retinal photoreceptors called Intrinsically Photosensitive Retinal Ganglion Cells detect ambient light changes, transmitting this to the master pacemaker in the SCN in the hypothalamus.
What is the function of the SCN?
Master pacemaker of circadian system, co-ordinating timing of physiolgoical processes/behaviours, based on input from light-dark cycles, thus stnchronizing timing of CR.
What happens in response to darkness?
Pineal gland production of melatonin, which decreases during the day.
Why is melatonin important?
Promotes sleep onset and consolidations, suppressed by exposure to blue light.
How is activity/stability of clock proteins regulated?
By PTM like phosphorylation and acetylation.
Why is phosphorylation important in clock protein regulation?
Nuclear entry, stability, and degradation of clock proteins.
How does the SCN maintain a molecular clock?
Neurons with robust circadian rhythms, driven by the molecular clockwork of Per and Cry.
How do these SCN neurons maintain one consistent rhythm?
Synaptic connections, gap junctions, and paracrine signalling mechanisms.
What are Phase Response Curves?
Depict magnitude and direction of phase shifts induced by light exposure at different times of the circadian cycle, with a biphasic pattern.
When do PRC phase advances occur?
When light exposure occurs during early subjective night, and phase delays occur when light exposure during late subjective night or early subjective day.
What is the biochemistry of phase shifts?
Light-induced phase shifts involve intracellular signalling pathways modulating clock gene activity and their protein products.
What do these Phase Shift signalling pathways do?
Involve second messenger systems, protein phosphorylation cascades, and gene expression changes influencing clock gene expression timing and CR phase.
