Circadian Rhythms Flashcards
The earth synchronizes our internal clock. True/false
True. The period is not under selection pressure but the phase
The internal clock is exactly 24 hours. True/ false
False. The internal clock is NOT exactly 24 hours
What is an example of behaviour of a plant that shows that circadian clocks help anticipate environmental cycles?
Sunflower leaves orientate towards the position of the sun. During the night, when the sun isn’t there, the leaves move towards the East anticipating sunrise
What are examples of rhythmic hormones?
cortisol
melatonin
Which hormone prepares the body from horizontal to vertical position?
Cortisol, for higher heart rate hence rises just before morning
Which hormone is only secreted when it’s dark?
melatonin- not a sleep hormone, secreted by pineal gland, used to treat jetlag
Why is the incidence of heart attacks and stroke highest between 6 am and 12 pm?
Due to increased levels of cortisol, increased heart rate may lead to high incidence of cardiovascular attacks
Why is it that in rheumatoid arthritis, pain and stiffness is greatest in the morning? And how can treatment optimize this timing?
Pro inflammatory cytokine rhythm peaks at 4 am. Treatment with glucocorticoids at 3/4 am to supress the immune system
When are asthma attacks most severe?
midnight
Define pharmacokinetics/ dynamics
kinetics: what the body is doing to the drug ie absorption/metabolism
dynamics: what the drug is doing to the body, whether the target structures of the drugs are rhythmic eg cox enzymes for asprin
French scientist that found out that mimosa leaves are upright during the day and drooped in darkness
De Marian
Founding father of chronobiology
Jurgen Aschhoff- investigated in a constant darkness ie WW2 bankers in Munich, having a low core body temperature correlated with sleep
What is the endogenous circadian period?
Approxiamtely 1 day can be 24.1 hours
Circadian clocks are endogenous self sustained oscillators. True/ false
True
Fundamental properties of circadian clocks
are endogenous, self-sustained oscillators
free running period/tau is close but not exactly 24 hours
Free-running periods are temperature compensated
rythmic environmental stimuli entrain circadian clocks
What is the master clock?
Suprachiasmatic nucleus SCN located in the hypothalamus above the optic chiasm
Evidence of the SCN being the master clock
loss of overt circadian rhythms in SCN lesions
transplantation of fetal SCN tissue in SCN lesioned arrhythmic host restores locomotor activity
Genotype of donor SCN determines circadian rhythm of host
SCN explants-neurons show self sustained circadian oscillations
How is the SCN linked to the retina?
retinohypothalamic tract
Circadian oscillator is cell autonomous.true/false
true. Each individual SCN neuron will have a 24 hr circadian rhythm as well as cell autonomous ie self sustaining
In which peripheral cells is the SCN also present
liver, kidneys. peripheral organs also show circadian rhythm
How is oscillation generated?
By -ve feedback. TF (+ve elements) activate transcription of mRNA into clock genes , which are negative elements eg period 1, 2, cry 1, that inhibit the transcription factors hence negative feedback.
-ve feeback loop causes delay hence oscillations
How do geneticists investigate molecular clockwork?
forward and reverse genetics
forward: from phenotype to gene eg id of the clock gene
reverse: from gene to phenotype eg differential function of the 2 cry genes
In mammals, light synchronizes circadian clock with the environment. True/ false
true. retina to SCN to regulation of physiology and synchrony of peripheral clocks
What is a chronotype
popensity of an individual to sleep at a particualr time during a 24 hour period. behavioural manifestation underlying circadian rhythms of physical processes
Define scissors of sleep
sleeping patterns on free days different from work days. sleep longer on free days to compensate for shorter sleep duration during work days eg for late chronotypes
for the early birds, light needs to delay because they have a fast circadian clock. True/false
True. fast circadian clock delay needs to be bigger than advance
for night owls, light needs to advance because they have a slow circadian clock/ True/false
true. slow circadian clock. Advance needs to be bigger than delay
Define entrainment
synchronization of the endogeneous oscillator to the light/dark cycle of the environment
how do rhythmic environmental stimuli entrain circadian clocks
period of the biological rhythm becomes equal to the external Zeitgeber rhythm with a stable phase angle
Which two processes regulate the timing of sleep
circadian process C
homeostatic process S- sleep dependent
