History of Circadian Rhythms

Question 1

Circadian

Answer 1

about the day, must:
- have a free-running period of 24hours
- entrainable to zeitgebers
- temperature-compensated

Question 2

Circadian rhythms

Answer 2

• rhythms remain even if external conditions are fixed
• loss of rhythms with disease (e.g. Alzheimer’s disease) and age
• increased risk of these diseases with shift workers and frequent travel across time zones

Question 3

Examples of circadian rhythms

Answer 3

• plants open and close
• wounds heal faster at night
• liver uses glucose differently

Question 4

Zeitgebers

Answer 4

time cues

Question 5

Zeitgeber time

Answer 5

external time
ZT00 = actual dawn
ZT12 = actual dusk

Question 6

Circadian time

Answer 6

internal time, independent of external cues
CT00 = subjective dawn
CT12 = subjective dusk

Question 7

Diel

Answer 7

daily

Question 8

Diurnal

Answer 8

day active

Question 9

Nocturnal

Answer 9

night active

Question 10

Clock mutants

Answer 10

grow best in an environment which matches their intrinsic periods

Question 11

Sleep

Answer 11

naturally recurring state in with decreased or absent consciousness, suspended sensory activity and inactivity of voluntary muscles

Question 12

Sleep threshold

Answer 12

• increased in day
• decreased at night

Question 13

Sleep debt

Answer 13

accumulate sleep debt if do not sleep

Question 14

Sleep threshold and sleep debt

Answer 14

• threshold and debt create the sleep/wake cycle
• if do an all-nighter, initially difficult due to low sleep threshold
• once overcome this, can make it through the night, as sleep debt is building but threshold is high

Question 15

Importance of circadian rhythms

Answer 15

• anticipate environmental changes
• temporal partitioning in DNA synthesis to a phase in which radiation-induced damage is less likely
• temporal separation of antagonistic processes e.g. protein synthesis and degradation

Question 16

Bu:nning hypothesis

Answer 16

circadian rhythms come from interaction between external stimuli and internal oscillator

Question 17

Ascoff’s rule

Answer 17

under constant conditions, circadian rhythms free run at less than 24hrs for nocturnal and more than 24hrs for diurnal species

Question 18

Jetlagged bees experiment

Answer 18

• bees transported from Paris to New York under constant conditions
• didn’t entrain as under constant conditions, so came out for food at Paris time
• moved to California under non-constant conditions
• came to collect food at 2 times: original Paris time (due to endogenous clock) and new California time (due to entraining to external cues)

Question 19

Bunker experiments

Answer 19

• isolated people in bunkers
• couldn’t access external conditions, but could change their own light levels
• conditions aren’t constant but are based on their own circadian rhythms
• circadian rhythm persisted and so must be endogenous
• changes in body temperature, salt levels are circadian

Question 20

Early recognition of circadian rhythms

Answer 20

• different plants open and close at different times of the day
• continues in constant dark
• bees came out every day at time when marmalade on toast eaten
• even when no marmalade
• so must be endogenous