Rhythms of Life

Book Notes on Chronobiology and Photoperiodism.

Rhythms of Life – the Biological Clocks that Control the Daily Lives of Every Living Thing (2004) by Russell G. Foster & Leon Kreitzman

p2 “The big difference between us and other living things is that to some extent we can cognitavely override these ancient hard-wired rhythms. Instead of sleeping as our bodies dictate, we drink another cup of coffee, turn up the radio, roll down the car window and kid ourselves that we can beat a few billion years of evolution.”

“When [daily circadian rhythm] is disrupted we suffer from the relatively mild symptoms of jet-lag through to serious and poetntially life threatening conditions such as depression and sleep disorders.”

p3 “[Biological clocks]… are reset at sunrise and sunset each day to link astronomical time with an organism’s internal time.”

p5 “All of us in the developed world now live in a ’24/7′ society. This imposed structure is in conflict with our basic biology. The impct can be seen in our struggle to balance our daily lives with the stresses this places on our physical health and mental well-being. We are now aware of this fundamental tension between the way we want to live and the way we are built to live.”

[see Colin Pittendrigh]

p38 “Every atom in our bodies is oscillating at around 1016 Hz.”

“The rods and cones in the retina respond to light oscillating at between 1015 – 1014 Hz. The brain’s electrical activity…has a frequency of 101 Hz… The heart beats at approimately 100 Hz…and respiration occurs at about one breath every six seconds.”

p97 “Although at some level everything about a simple living organism is implied in its genes, on the other hand, you really have to understand the products of the genes and how they interact, which is more complex than just knowing the sequence of the genes.” –Clyde Hutchenson (1999)

p102 “Anticipation is the key to…biological survival and hence success… The anticipation we are talking about is deeper and more profound because it tunes in an organism to its broader environment. Francois Jacob, one of the great pioneers of molecular biology, said, “one of the deepest, one of the most general functions of living organisms is to look ahead, to produce a future.”


  • the VLPO (ventrolateral preoptic nucleus) of the anterior hypothalamus promotes sleep. Neurones from this nucleus release GABA (gamma-amino butyric acid), an inhibitory neurotransmitter of the nervous system. The neurones project to and inhibit the activity of the nuclei of the ascending arousal system, and the lateral hypothalamus (LH).
  • The ascending arousal system (AAS) of the brainstem and hypothalamus promotes wakefulness in the forebrain. Neurones from five regions in this complex (LDT, PPT, DR, LC, TMN) release several excitatory neurotransmiters. In the brainstem, neurones from teh LDT (laterodorsal tegmental nuclei) and PPT (pedunculopontine tegmental nuclei) project to the thalamus, and from there to the forebrain. These two nuclei are responsible for the release of acetylhoine. The LC (Locus coeruleus), also in the brainstem, has neurones that project the forebrain and release noradrenaline. the DR (dorsal raphe nucleus) of the brainstem has neurones that project to the forebrain and release serotonin In the hypothalamus, neurones from the TMN (tuberomammillary nucleus) project to the forebrain and release histamine.
  • The lateral hypothalamus also promotes wakefulness. Neurones from this nucleus release orexin (also called hypocretin), a very recently discovered neuropeptide. Neurones project to the nuclei of the ascending arousal system, the forebrain, as well as the VLPO.
  • The NREM/REM oscillator is a cluster of five separate nuclei in the brainstem that provides the switch between NREM and ReM sleep. Three of these nuclei, the LDT, PPT and BRF (brainstem reticular formation), are interconnected and excite the activity of both themselves and the two other nuclei involved in the NREM/REM oscillator. the LC and DR form a second functional unit. .The LC and DR are interconnected and inhibit the activity of both themselves and the LDT, PPT and BRF functional unit. This reciprocal set of interactions generatess a flip-flop switch that produces a roughly 90-minute oscillation in NREM and REM sleep.
  • The suprachiasmatic nuclei (SCN) regulate the various sleep structures of the brain either directly by neural or chemical outputs, or indirectly by teh release of the pineal hormone melatonin. Melatonin is high throughout the night, and when administered has been shown to increase the propensity for sleep in humans.

Rhythms in Humans





00:00-02:00 ↑sleep initiation

↓gastric motility


↑cerebral infarction

↑growth hormone

↑uric acid concentration

02:00-04:00 ↑gastric ulcer crises

↑gall bladder symptoms↑asthma



↑triacyl glycerol



04:00-06:00 ↓body temperature


↓deepest sleep

↓urine production


↑gastric ulcer crises









06:00-08:00 ↑sleepiness/tiredness ↑rheumatoid arthritis

↑allergic rhinitis







↑plasma catecholamines

↑fight or flight system

↑platelet viscosity

↑blood viscosity

↓fibrinolytic activity

↑NK-Cell activity

08:00-10:00 ↑bowel movement

↑blood pressure

↑heart rate

↑myocardial infarction


10:00-12:00 ↑concentration

↑Short-term memory

↑logical reasoning

↑blood pressure

↑myocardial infarction



12:00-14:00 ↑concentration

↑short-term memory

↑logical reasoning

↑urine production

↑airway patency

14:00-16:00 ↑insulin
16:00-18:00 ↑osteoarthritis


18:00-20:00 ↑body temperature


↑cardiovascular efficiency

↑muscle strength


↑grip strength

↓sleep propensity

20:00-22:00 ↑gastric acidity ↑skin sensitivity

↑menopausal flushes

303 Days to Dec 21st 2012


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