Lecture Notes Chronobiology (WLBS19002)

Chronobiology
Chapter 1 Overview of Biological Timing from Unicells to Humans
Lecture 1A Clock as concepts

The concept of time:
- Time passes only in one direction
- Time has directionality
Daily time  clocks (oscillator)
Seasonal time  Stonehenge, prehistoric measurements ~2500 BC.

Oscillatory process: something that goes up and down.
Energy is needed to maintain a stable oscillation
Relaxation oscillator (is not a clock):
- Hour glass: energy is needed to start the oscillatory process. Forget to turn it around 
disturbance of process (delay)
- Persian water clock




The brain does not use a relaxation oscillator  it continues a normal pattern whether you sleep or
don’t sleep.

Sun dial: used to measure local solar time
Zonnewijzer prinsentuin Groningen
Su Sung’s water tower clock is a true clock with continuous flow of energy. It is not dependent on a
single moment of energy (energy is stored).
The swinging chandelier in the cathedral of Pisa (Galileo Galilei)
- Duration of one oscillation is dependent of amplitude
Pendulum clock (Christiaan Huygens)
- Length of arm determines the period of the swing
- T0 is time it takes for one swing to complete




Christiaan Huygens:
- Invented Pendulum Clocks based on Galilei’s pendulum theory
Discovered ‘entrainment’ between two coupled oscillators  Entrainment: synchronization of one
oscillator towards another.

The pendulum is temperature dependent, slow movement when candles are lit/ slow movement in
summer.
The longitude problem: Knowledge of both latitude and longitude required on a ship
The latitude was maintained, but longitude was undetermined.
 Harrison’s clock = temperature compensated.

Circadian clock is mostly influenced by light/dark.
Organisms can be unrhythmic but still survive.

,Clocky:
- No food during night  anticipation of coming night causes more food intake. This requires
the circadian clock.
It is beneficial for animals to anticipate dawn and dusk and therefor to have a circadian clock.

Lecture 1B Clocks in nature

Discovery of daily rhythms
- 325 BC by Androsthenes Thasius
- Following the cycle of day and night (24h) by studying the leaf movements of Tamarindus
Indicus.
Linnaeus’ Flower Clock 1751: shows the hours in terms of flower opening
Higher plants possess circadian rhythms of photosynthesis  exhibit endogenous daily leave
movements.

Discovery of circadian rhythms
- Biological rhythms persist without light  1729: De Marian: leave movements in Mimosa
Pudice
- Intrinsic period ~24h  1832: De Candolle: leave movements in Mimosa continued in
continuous darkness.
- 1926: Johnson: mammalian circadian rhythms in Peromyscus maniculatus  first
observation of freerunning circadian rhythm in behaviour in a mammal
Mimosa Pudice:
- Sensitive plant, will close it leaves when being touched, to reduce energy loss.


Overdag staan ze
open en in de nacht gaan
ze dicht. De Mairan deed
experiment met deze
plant, zeKe hem in
gesloten
donkere kast. Maar de
cyclische opening/sluing
van de bladeren ging door

,Overdag staan ze
open en in de nacht gaan
ze dicht. De Mairan deed
experiment met deze
plant, zeKe hem in
gesloten
donkere kast. Maar de
cyclische opening/sluing
van de bladeren ging door
- During day: open, during night: closed
- Cyclic opening/closing continued during DD

Karl von Frisch ‘Time memory’
Bees can be trained to return to same feeding place at a certain time of day (even when no food is
offered). Bees tell each other by a pattern where the food is located. They adapt to the location of
the sun.
Gustav Kramer  migrating starlings use a sun-compass. This is time-compensated, so starlings have
a biological clock.




Nocturnal animal




Woodland Hastings  unicellular organisms can have circadian rhythms and circannual rhythms.

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