1. BIOLOGICAL RHYTHMS
Presented by
Dr. B. Victor., Ph. D
Email : bonfiliusvictor@gmail.com
Blog: bonvictor.blogspot.com

2. Presentation outline
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Ethology and Chronobiology.
Biological rhythms – introduction, definition,
parameters, properties and general criteria.
Zeitegebers – definition and examples.
Classification of biorhythms.
Types and examples of biorhythms.
Circadian rhythms-explanation and properties.
Human biorhythms- explanation, types and examples.
Circadian pace maker – master clock.
Theories of biorhythms –endogenous and exogenous
.
Disorders and therapies.

3. Ethology
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Ethology is the study of animal behavior in a
normal environment.
The term „behavior‟ denotes “what an
organism does”
All behavior patterns are co-ordinated
sequences of neuromuscular activity.

4. Chronobiology
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Chronobiology is a field of biology that
examines periodic phenomena in the
biological processes of living organisms.
“chrono” means related with time; „biology‟
means science of life.
Thus chronobiology is the study of science of
life in relation with time
„biological rhythmicity‟ is an integral part of the
organization of living matter.

5. Biological rhythms-Introduction
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Biological rhythms are an integral part of every
day life for most organisms on earth.
They regulate most important functions in each
organism.
In plant circadian clocks control flowering,
response to seasons and photosynthesis.
In mammals, circadian clocks manage
sleeping, waking, feeding and controlling
whether an animal is nocturnal or diurnal.

6. Behavior rhythms-definition
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A rhythm has been defined as a sequence of
events that repeat themselves through time in
the same order and the same interval.
Simply a rhythm is a periodically recurring
event.
Many behavioral patterns of organisms are
subject to rhythmic variations in response to
various external geophysical rhythms in the
environment.

7. Biological rhythms- definition
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Biological rhythms are those rhythms that
arisen in organisms to match external
geophysical rhythms with comparable
period(Chandra sekaran 1986).
A biorhythm means a periodic occurrence of
specific physiological changes in living
organisms.
The majority of organisms show daily and
Crepuscular=twilight
annual cycles of activity and development.
Diurnal= day active
Nocturnal=night active
active

8. Parameters of biological
rhythms
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Each biological rhythm is composed of repeating
units called cycles.
The length of time required to complete an entire
cycle is the period.
The magnitude of the change in activity rate
during a cycle-the difference between peaks and
toughs is the amplitude.
Any specified recognizable part of a cycle is
called a phase.

9. Properties of biological rhythms
Biorhythms have self – sustaining
pacemaker mechanism.
Biorhythms maintain their normal cyclicity
even in the absence environmental cues
Biorhythms are unaffected by metabolic
poisons or inhibitors.
Biorhythms are genetically transmitted.

10. General criteria of biological
rhythms
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The rhythms repeat in a given time period for
e.g. circadian rhythms in every 24 hours.
The rhythms persist in the absence of external
cues.
The rhythms can be adjusted to match the
local time ( entrain able ).
The rhythms maintain circadian periodicity
over a range of physiological temperatures.

11. Endogenous biorhythms
1.Circadian daily
Circa tidal –
sea tide
Circannual annual
Circulunar –
moon phase

12. Zeitgebers=time givers =
synchronizers
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The mechanism whereby the period of a rhythm
occurs repetitively and coincides approximately
with the presence of some external stimulus is
called entrainment.
Cues that provide information to animals about
periodicity of environmental variables are
Zeitgebers.
Zeitgebers are the entraining agents defined as
those cyclic environmental cues that can entrain
free running endogenous pace makers.
Zeitgebers can influence rhythms by effecting
both the phase and the frequency.

13. Zeitgebers -examples
Animals
Zeitgeber
Terrestrial organisms
Daily light – dark cycles
Intertidal marine animals Ebb and flow of tides
Ectotherms-lizards,
insects
Small mammals
Temperature, light
Cycles of food
availability, social cues
=environmental cues

14. Zeitegebers -examples
temperature
Food
availability
Light
intensity
Social
interactions
zeitegebers

15. Classification of biorhythms -1
Physical classification(period of oscillation)
Functional
classification
(periodic physiological
factors)
Mathematical
Classification
(numerical
frequencies)
• Circadian-24h
• Ultradian-less than 20h
• Infradian- more than 28h
• Alpha rhythm
• Beta rhythm
• Gamma rhythm
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Qualitative
Punctual
Discrete
episodic

16. Classification of biorhythms -2
Descriptive
classification
• Diurnal, Nocturnal, Serotine, Vesperal
• Morning, Daily,
• Weakly, Monthly, yearly
Physiological
Classification
• Essential rhythm
• Non-essential rhythm
Duration
classification
• Permanent rhythm
• Temporary rhythm

17. Classification of biorhythms -3
Biological
• Conservative rhythms
classification • Reproductive rhythms
Resistance • Resistant rhythm
classification • Labile rhythm
Ontogenetic • Immature rhythms
classification • Mature rhythms

18. Classification of biorhythms -4
Consistency
classification
• Real rhythms
• Virtual rhythms
Hierarchical
classification
• Independent rhythms
• Dependent rhythms

19. Classification of biorhythms -5
Endogenous
rhythms
Exogenous
rhythms
• Circadian rhythms, tidal rhythms
• Lunar rhythms, semi-lunar
rhythms
• Circannual rhythms
• Light intensity rhythms,
temperature rhythms, pressure
rhythms,
• geophysical rhythms

20. Classification of biorhythms -6
Biological
rhythms
• Shot term rhythms
• Circadian rhythmsFeeding ,activity, hunger and
sleeping rhythms
• Long term rhythms
• Lunar, semi-lunar, tidal,
circannual, life cycle,
breeding, migration rhythms

21. Types and examples of
biorhythms
Epicycles
• Arenicola marina-lug worm-living in sand
flats of intertidal zones.
• Feed every 6 to 8 min
Epicycles
• Microtus species, small mammal show
bursts of activity by periods vary from 12 to
20 min.

22. Types and examples of
biorhythms-2
Circa tidal rhythms
• Mytilus edulis- marine mussels opening the
shell valves corresponding to the tides
Circa tidal rhythms
• Uca pugnax , fiddler crabs active during low
tides
Circa tidal rhythms
• Carcinus maenas –shore crabs show daily
activity based on tidal rhythms

23. Types and examples of
biorhythms-3
Lunar rhythms
• Eunice species – polalo worm –reproductive
activity is based on last quarter of lunar cycle.
Lunar rhythms
• Aplysia species – sea horse – daily activity is
based on half of lunar cycle.
Lunar rhythms
• Poecilia reticulata – fresh water guppy –spectral
sensitivity is based on lunar cycle.

24. Types and examples of
biorhythms-4
Circadian rhythms
• Sleep/wake cycle, mental alertness and eating habits in
humans are based on day and night cycles.
Circadian rhythms
• fruit flies (Drosophila melanogaster) hatch in greatest
numbers just at dawn.
Circadian rhythms
• Young dragon flies fly at dawn and adults fly during the
day.

25. Circadian rhythms
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A rhythm with a periodicity of 24 hours is
called a circadian( from Latin circa ‘about’; di
means day i.e. about a day) . E.g. sleep-wake
cycle.
There may be over 100 physiological cycles in
human body.
Circadian rhythms are endogenous.
Circadian rhythms present even in the
absence of environmental cues such as light,
temperature or social cues.

26. Properties of circadian rhythms
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They are genetic in origin.
They are controlled by biological clocks.
The biological clocks are reset and calibrated
by periodic environmental signals ( called
synchronizers or Zeitgebers or entraining
agents).
There are often cycles within cycles, their
intensity and frequency varying in different
parts of the activity period.

27. Human rhythms
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Human body appears to be a clock – shop.
There are several rhythms – one clock basis.
Most of the rhythms are interdependent and
coupled.
There may be one master clock orchestrating
all individual biological clocks.

28. Human being biorhythms
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Human biorhythms start from the moment a
person is born.
Most biorhythms are circadian.
Certain biorhythms are the natural monthly
fluctuations that govern physical, emotional
and intellectual aspects of human beings.
Human beings have three biorhythms:
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Physical biorhythm -23 days.
Emotional biorhythm – 28 days
Intellectual biorhythm – 33days

29. Hormonal (endocrine) circadian
rhythms
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Growth hormone –increase during sleep;
decrease during wakeful state.
Cortisol-highest during morning; lowest
during sleep.
Prolactin –resembles like growth hormone
cycle.
Aldosterone – peaks in afternoon; declines in
evening.
Testosterone – low in afternoon; high in night.

30. Human circadian rhythms
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Activity/rest cycle
Alertness cycle
Brain activity cycle
Blood pressure
Cardiovascular
performance
Catecholamine levels
Cortisol levels
Endocrine levels
Testosterone levels
Thyroxine levels
Insulin levels
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Endotoxin susceptibility
Ethanol metabolism
Prolactin levels
Pituitary activity
EEG
Gastrointestinal rhythms
Gonadal hormones
Heart rate
Pulse rate
Melatonin levels
Pineal activity

31. The circadian pace maker or
master clock
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The master clock controls circadian rhythms.
It consists of a group of brain cells in the
hypothalamus called supra chiasmatic
nucleus (SCN).
The hypothalamus continually measures the
light exposures via the retinal hypothalamic
tract and accordingly adjusts the timing of the
sleep-wake cycle.

32. Theories –endogenous rhythm
theory
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This concept suggests the biochemical nature
of clock mechanism.
The internal biological clock operate by cyclic
biochemical reactions.
The biochemical endogenous clocks are
sensitive to environmental cues.

33. Exogenous rhythm theory
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According to this theory, intracellular rhythm
occurs in response to cyclic geophysical
changes.
Brown (1970) conceptualized the system has
a two-layered ring.
There is a core of unchanging geophysical
cycles existing under a changeable system of
factors like light, temperature and food.

34. Rhythm disorders
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Seasonal affective disorder – SAD-is an
infradian rhythm disorder. SAD may have
disturbance in the melatonin system. Sad
people show low mood effects in winter
months.
Jet lag- influences our endogenous pace
maker.
Symptoms include tiredness, sleepiness, loss
of concentration, anxiety, depression and
irritability.
Some people recover quickly but others the

35. Chronotherapy
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Chronotherapy refers to the use of circadian
or other rhythmic cycles in the application of
therapy.
the treatment of an illness or disorder by
administering a drug at a time of day believed
to be in harmony with the body's natural
rhythms.
Chronotherapy is used in the treatment
of sleep disorders, asthma,
cancer, hypertension, and multiple types
of depression, seasonal affective

36. Summary
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All behavior patterns are co-ordinated
sequences of neuromuscular activity. A rhythm
is a periodically recurring event.
chronobiology is the study of science of life in
relation with time.
The majority of organisms show daily and
annual cycles of activity and development

37. About the presenter
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Dr. B. Victor is a highly experienced postgraduate
professor, retired from the reputed educational institution St. Xavier‟ s College(Autonomous), Palayamkottai, India627001.
He was the dean of sciences, assistant controller of
examinations and coordinator several academic research
workshops.
He has more than 32 years of teaching and research
experience
He has taught a diversity of courses and published 45
research articles in reputed national and international
journals.
Send your comments to : bonfiliusvictor@gmail.com