BIOLOGICAL RHYTHMS: IT

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BIOLOGICAL RHYTHMS ITS A MATTER OF TIME
Text Rhythms of Life Russell Foster and Leon
Kreitzman
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• What are Biological Rhythms?
• What are Rhythms?

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What is a rhythm?
Pattern Sequence Regularity Progression Time Measu
re Beat
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Rhythm sequence of events that repeat
themselves in the same order and with the same
time interval, over and over again. Biological
rhythm a biological event or function with a
pattern of activity that is repeated over and
over again at a constant time interval.
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What are examples of Biological Rhythms?
Biological Rhythms Heart rate Breathing Hormone
secretion Menstrual cycle Body temperature Sleep/w
ake cycle

Time
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• Biological Rhythms are the product of an
  internal biological timekeeping system which is
  controlled by a biological clock
• Chronobiology

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• Two Broad Categories of Biological Rhythms
• high frequency
• Ultradian
• Those that have a constant relationship with
  environmental rhythms
• Have a geophysical counterpart

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• ENVIRONMENTAL RHYTHMS
• Semi-Daily Rhythms
• Tidal
• Daily Rhythms
• Solar
• Monthly
• Lunar
• Quarterly
• Seasons
• Annual
• Longer than a year

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Spinning of earth on its axis
24h solar day Movement of earth
around sun 365 days
year Tilting of earth on its axis
seasons Movement of moon
around earth 24.53 days
lunar month
24.8h
lunar day
Geophysical
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Types of biological rhythms with a geophysical
counterpart
PeriodLength Name Chronobiological Name Example
12.4 h tidal CIRCA TIDAL crab activity on shoreline

29 days monthly CIRCA LUNAR menstrual cycle, marine reproduction.
365 days yearly CIRCANNUAL Hibernation, many reproductive cycles.
24 h daily CIRCADIAN (circa diem) sleep-wake cycle and many others
infradian
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What Kind of Organisms Have Biological Rhythms?
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• What is the purpose of having a biological
  timekeeping system?
• Promotes organisms ability to survive by
  coordinating its activities
• with changes in the environment
• Coordinates internal processes

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STROMATOLITE
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Many organisms have several kinds of biological
rhythms
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Alexander the Great 4th Century BC Tamarind Tree
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de Mairan, 1729
endogenous
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Du Monceau 1759 Circadian rhythms do not
depend on temperature changes Linneaeus 1751
Circadian rhythms are genetically determined
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Linneaeus 1751
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de Candolle 1832 When not exposed to
environmental day/night rhythms plant leaves
opened and closed on a 22 23 h cycle instead of
a 24 h cycle Free-running rhythm
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• Circadian rhythms are endogenous.
• Endogenous rhythms are not exactly 24h.
• The periods of Circadian rhythms are genetically
  determined.
• Endogenous rhythms are temperature-compensated

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Bees 1910 Forel 1929 Beling
1950s Renner Drosophila 1950s
Pittendrigh
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PACEMAKER
TARGET TISSUE
BIOLOGICAL RHYTHMS (overt rhythms)
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ZEITGEBER
TRANSDUCER
PACEMAKER
Endogenous, free-running rhythm
INTERMEDIATE ELEMENTS
TARGET TISSUES
BIOLOGICAL RHYTHMS
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Activity (locomotor) rhythm
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Chronobiology Biological rhythm Ultradian Infradia
n Circadian Circatidal Circalunar Circannual Endog
enous Free-running Pacemaker Target tissue Overt
rhythm Nocturnal Diurnal LL DD LD 1212
Study of biological timekeeping Cyclical,
repeated variation in a biological function High
frequency repeats many times in a day Repeats
at intervals much longer than 24
hours Approximately a day (24 hours) Approximately
every 12.4 hours ( with the tide) Approximately
once a month Approximately once a year Internally
generated rhythm Not synchronized to external
signals A structure that generates a
rhythm Tissue whose function is regulated by the
pacemaker A visible, measurable rhythm Active at
night Active during the day Constant
light Constant darkness 12 hours of light 12
hours of dark