Biological Rhythms and its Hormonal Control

Biological Rhythms

• predictable fluctations resulting from seasons, time of day, etc.
• cycles can link to patterns operating at different time frames: circadian (24h period length), ultradian (>24h), tidal (12.4h), lunar (24.8h), circannual (12months); exogenous vs. endogenous cycles
• Description of a rhythmic pattern: sequence of events which repeat in cyclical fashion, cycle, frequency, amplitude
• Biological clocks are self sustaining oscillators, that is linked to and can be reset by the environment
• "Free-running" cycles, Entrainment, Zeitgeber
• Circadian clocks with at least three elements
  • input pathway(s) relay environmental information to a circadian pacemaker
  • endogenous pacemaker (oscillator) generates temporal patterns
  • output pathway(s) through which the pacemaker regulates various output rhythms
• periodic expression of immediate early genes (IEG), period (per) and timeless (tim) genes control each other through transcription-translation autoregulatory feedback loop in Drosophila
• Pineal gland, and Melatonin in photoperiod
• Mammalian suprachiasmatic nucleus or SCN

Reading Assignment

• Chapter 9: Biological Rhythms. pp 142-156

Food for Thought

Why does the ruby-throated hummingbirds migrate from Ohio to Belize and back?

Links of interest

• Cicadas of Michigan
• Biological Time-keeping
• Light Sets the Molecular Controls of Circadian Rhythm
• Take the Lark and Owl Test
• Faculty Profile and Research Interests of Mike Geusz, Biology, BGSU
• Melatonin and its Effects