biological rhythms: it’s a matter of time
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BIOLOGICAL RHYTHMS: IT’S A MATTER OF TIME
Text: Rhythms of Life
Russell Foster and Leon Kreitzman
• What are Biological Rhythms?
• What are Rhythms?
Pattern
Sequence
Regularity
Progression
Time
Measure
Beat
What is a rhythm?
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.
Biological Rhythms
Heart rate
Breathing
Hormone secretion
Menstrual cycle
Body temperature
Sleep/wake cycle Time
What are examples of Biological Rhythms?
• Biological Rhythms are the product of an internal biological timekeeping system which is controlled by a biological clock
•Chronobiology
•
Two Broad Categories of Biological Rhythms
•high frequency –
•Ultradian
•Those that have a constant relationship with environmental rhythms –
•Have a geophysical counterpart
ENVIRONMENTAL RHYTHMS
Semi-Daily Rhythms•Tidal
Daily Rhythms•Solar
Monthly•Lunar
Quarterly•Seasons
Annual
Longer than a year
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
Types of biological rhythms with a geophysical counterpart:
PeriodLength
NameChronobiological
NameExample
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
What Kind of Organisms Have Biological Rhythms?
What is the purpose of having a biological timekeeping system?
Promotes organism’s ability to survive by coordinating its activities
with changes in the environment
Coordinates internal processes
STROMATOLITE
Many organisms have several kinds of biological rhythms
Alexander the Great
4th Century BC
Tamarind Tree
de Mairan, 1729
endogenous
Du Monceau 1759
Circadian rhythms do not depend on temperature changes
Linneaeus 1751
Circadian rhythms are genetically determined
Linneaeus 1751
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
•Circadian rhythms are endogenous.
•Endogenous rhythms are not exactly 24h.
•The periods of Circadian rhythms are genetically determined.
•Endogenous rhythms are temperature-compensated
Bees – 1910 Forel
1929 Beling
1950s Renner
Drosophila – 1950s Pittendrigh
PACEMAKER
TARGET TISSUE
BIOLOGICAL RHYTHMS (overt rhythms)
ZEITGEBER
TRANSDUCER
PACEMAKER
INTERMEDIATE ELEMENTS
TARGET TISSUES
BIOLOGICAL RHYTHMS
Endogenous, free-running rhythm
Activity (locomotor) rhythm
Chronobiology
Biological rhythm
Ultradian
Infradian
Circadian
Circatidal
Circalunar
Circannual
Endogenous
Free-running
Pacemaker
Target tissue
Overt rhythm
Nocturnal
Diurnal
LL
DD
LD 12:12
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
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