Biological rhythms

cyclical activity which is a characteristic of all animal life -the study of biological rhythms is called chronobiology

endogenously generated rhythms with a period close to 24 hours

a circadian rhythm that is synchronized with the day/night cycle

Biological rhythms with a period much shorter that that of a circadian rhythm

biological rhythm with a cycle of more than 24 hours eg- the human menstrual cycle

endogenous pacemaker (body clocks)

Exogenous zeitgebers-these are rhythmically occuring natural phenomenon which acts as a cue to regulate circadian rhythm

de mairan experiment with mimosa pudica plant -plant put in total darkness continued to open and close flowers

-professor nathianel kleitman and bruce richardson spent 32 days underground in a cave -no natural sunlight -measured body temperature, urine output. eating habits and sleeping patterns

-despite no daylight or other external cues to the world they maintained a regular sleep-wake cycle. -humans have an endogenous circadian rhythm -its approx 24 hours but not exactly 24 hours

-konopka and benzer discovered the period gene (PER) in drosophilla influencing biological rhythms -research in 1960/70s concluded that natural circadian rhythm in humans was 25hrs not expected 24hrs -length of rhythms dependent on PER3 gene

individuals have the propensity to sleep at different times during the day

the most important zeitgeber is light -these synchronize the internal body clock with external time

the suprachiasmatic nucleus (SCN) which is located close to the optical nerves and this is a good position to be adjusted by sunlight.

-key endogenous pacemaker -located in the hypothalamus -hypothalamus comprised of several nuclei -SCN has intrinsic activity rhythm even if isolated from rest of brain -lesion of the SCN- circadian rhytms disrupted-stephan and zucker 1972

-Ralph et al 1990 -removed SCN from mutant hamster with natural sleep wake cycle of 21 hrs -implanted from non mutant hamster with 24 hr cycle -hamsters with implanted SCN changed to 21hr cycle -concluded that SCN is the dominant endogenous pacemaker

-suprachiasmatic nucleus communicates the circadian rhythm to body via melatonin production -pineal gland stores and releases melatonin -melatonin production increases steadily after dusk and reduces during sleep -melatonin does not induce sleep but simply signals the start of the sleep process -melatonin tablets can help with jet lag

-hypersomnolence -headaches -insomnia -difficulty concerntrating -impaired judgement -mild nausea

-biological clock is behind local time -body not ready for sleep -takes longer to adjust