BIOLOGICAL RHYTHMS: ITS A MATTER OF TIME Text: Rhythms of Life Russell Foster and Leon Kreitzman What are Biological Rhythms? What are Rhythms? What is a rhythm? Pattern Sequence

Regularity Progression Time Measure Beat 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. What are examples of Biological Rhythms? Biological Rhythms Heart rate Breathing Hormone secretion Menstrual cycle

Body temperature Sleep/wake cycle Time 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: Period Length 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 What Kind of Organisms Have Biological Rhythms? 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 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 1929 Forel Beling

1950s Renner Drosophila 1950s Pittendrigh PACEMAKER TARGET TISSUE BIOLOGICAL RHYTHMS (overt rhythms)


TARGET TISSUES BIOLOGICAL RHYTHMS Activity (locomotor) rhythm Chronobiology Study of biological timekeeping

Biological rhythm Cyclical, repeated variation in a biological function Ultradian High frequency repeats many times in a day Infradian

Repeats at intervals much longer than 24 hours Circadian Approximately a day (24 hours) Circatidal Approximately every 12.4 hours ( with the tide)

Circalunar Approximately once a month Circannual Approximately once a year Endogenous

Internally generated rhythm Free-running Not synchronized to external signals Pacemaker A structure that generates a rhythm

Target tissue Tissue whose function is regulated by the pacemaker Overt rhythm A visible, measurable rhythm Nocturnal

Active at night Diurnal Active during the day LL Constant light

DD Constant darkness LD 12:12 12 hours of light; 12 hours of dark

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