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Biological rhythms

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.

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Biological rhythms

  1. 1. BIOLOGICAL RHYTHMS Presented by Dr. B. Victor., Ph. D Email : Blog:
  2. 2. Presentation outline           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. 3. Ethology    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. 4. Chronobiology     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. 5. Biological rhythms-Introduction     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. 6. Behavior rhythms-definition    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. 7. Biological rhythms- definition    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. 8. Parameters of biological rhythms     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. 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. 10. General criteria of biological rhythms     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. 11. Endogenous biorhythms 1.Circadian daily Circa tidal – sea tide Circannual annual Circulunar – moon phase
  12. 12. Zeitgebers=time givers = synchronizers     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. 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. 14. Zeitegebers -examples temperature Food availability Light intensity Social interactions zeitegebers
  15. 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 • • • • Qualitative Punctual Discrete episodic
  16. 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. 17. Classification of biorhythms -3 Biological • Conservative rhythms classification • Reproductive rhythms Resistance • Resistant rhythm classification • Labile rhythm Ontogenetic • Immature rhythms classification • Mature rhythms
  18. 18. Classification of biorhythms -4 Consistency classification • Real rhythms • Virtual rhythms Hierarchical classification • Independent rhythms • Dependent rhythms
  19. 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. 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. 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. 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. 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. 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. 25. Circadian rhythms     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. 26. Properties of circadian rhythms     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. 27. Human rhythms     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. 28. Human being biorhythms     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:    Physical biorhythm -23 days. Emotional biorhythm – 28 days Intellectual biorhythm – 33days
  29. 29. Hormonal (endocrine) circadian rhythms 1. 2. 3. 4. 5. 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. 30. Human circadian rhythms            Activity/rest cycle Alertness cycle Brain activity cycle Blood pressure Cardiovascular performance Catecholamine levels Cortisol levels Endocrine levels Testosterone levels Thyroxine levels Insulin levels            Endotoxin susceptibility Ethanol metabolism Prolactin levels Pituitary activity EEG Gastrointestinal rhythms Gonadal hormones Heart rate Pulse rate Melatonin levels Pineal activity
  31. 31. The circadian pace maker or master clock    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. 32. Theories –endogenous rhythm theory    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. 33. Exogenous rhythm theory    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. 34. Rhythm disorders     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. 35. Chronotherapy    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. 36. Summary    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. 37. About the presenter      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 :
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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.


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