Module 1: Introduction to Biological Rhythms

what is the greek word for time?

chronos

what is the greek word for life?

bios

what is the greek word for study?

logos

what does chronobiology study?

• biological rhythms in hours, days, months and years range

what are circadian rhythms?

internal 24h biological clocks that synchronize our behavior and physiology with the solar day

what are the three main learning objectives?

• understand why biological clocks and rhythms exist

• understand how biological clocks work

• understand the role of biological clocks in normal behavior and physiology and the relevance of biological clocks to human health and welfare

what is a biological rhythms?

a process that repeats at regular intervals

what is a period (tau)

amount of time required to complete one full cycle

what is the greek word for wavelength?

lambda

what is the frequency?

cycles per unit time

ultradian

rhythms with a period much less than 24 h

daily rhythms

rhythms period of 24 h

infradian

rhythms with a period much longer than 24 h

what is the special desgination ‘circa’ rhythms?

the periods approximate a naturally occurring cycle in the environment

circatidal

approximately 12.5 h ultradian rhythms that match the tides

circalunar

approx. 29.5 day infradian rhythms that match the lunar month

circannual

approx. 365 day infradian rhythms that match the solar year

why are the four ‘circa’ rhythms unique?

• each approximates the periodicity of a geophysical, environmental cycle

• each can persist for many cycles in the absence of the geophysical cycle

what are the two implications of rhythms persisting in the absence of environmental cycles?

• generated by internal, endogenous timekeeping which runs at a rate that approximates corresponding environmental cycle

• environmental stimuli must modify the biological clock so that it is stably synchronized to the outside world

which physician/scientist made an effort to describe daily rhythms in behavior and physiology?

Franz Halberg

what did Halberg and his team measure?

physiological variables in mice and humans at multiple times of day and found significant daily rhythms in the levels or rates of most of these processes

what is an acrophase?

peak of the cosine wave

what did the two Halberg graphs point out?

much of the biochemistry and physiology of mice and humans exhibit 24 hours rhythmicity and that different rhythms rise and fall at different times of day

are all daily rhythms such as rest, activity, food and water intake classified as circadian rhythms

no, all circadian rhythms are daily rhythms, but not all daily rhythms are circadian rhythms

how do you determine whether a daily rhythms is circadian or not?

must be shown to persist in the absence of 24-hour environmental cycles, such as light and dark

who discovered circadian rhythms?

Jean Jacque d’Ortous de Mairen

how did de Mairen discover circadian rhythms?

noticed that plants also seem to watch the sky and they open and closed their leave depending on the day-night cycle (Mimosa plant)

what was the experiment de Mairen do with the plants?

he moved the mimosa plants to a closet where they would be kept in the dark, and then took observations of the plants at regular intervals around the clock

what was the difference between de Mairen and de Candolle’s study?

de Candolle used a cave as a natural shield instead of a closet and found that the rhythm was not exactly 24 h but 23.8 h, suggesting that the leaf movements were caused by something in the environment that we cannot detect

what does Zeitgedachnis mean?

time-memory

what did Forel fighure out with the bees?

bees are able to learn and remember time of day even if the experiments are conducted deep in a salt mine, they appear to be using an internal clock

how did Renner expand upon the work of Beling (bee experiment)?

trained bees to find food at a feeder in New York, then flew them overnight to California where they flew to the feeder 3h early

what type of experiment did they conduct to appease skeptics?

sending bread mold (neurospora crassa) to space in race tubes, thus allowing to mold to produce a batch of spores every 24 hours

what did Carl Ludwig invent?

kymograph, it measures blood pressure in humans

How was the kymograph system used for rats?

they were placed in the rotating drum for recording locomotion and measures the activity levels and the effects of various stimuli

how did Richter study spontaneous behaviors in the absence of environmental stimuli?

he attached the kymograph to a cage and left them alone in a barren environment to move about, eat and drink spontaneously

what is an actogram or raster plot?

a graphical representation to measure an organism’s biological rhythm patterns. seen in Richter’s experiment with rats

free-running

rhythms that persists in a time-free environment

entrained

rhythm that is synchronized to an external time cue, by an active process

mechanism by which a rhythm can be synchronized to the outside world, involving the action of a time cue on the phase and period of the clock that controls the rhythm

alpha

daily active phaser

rho

daily rest phase

subjective day and night

day - portion of a free-running rhythm when the animal is behaving as if it is daytime

night - when the organism acts as if it is night time

zeitgeber time

external time

photoperiod

daily light period; duration of lights on

scotoperiod

daily dark period; duration of lights-off

what experiment was the first evidence of true circadian rhythms in humans

nathaniel Kleitman spent a month in a cave trying to live on 28h day but continued to express a sleep-wake cycle closer to 25h

sleep-dependent circadian rhythms in the body

examples include blood levels of growth hormone and prolactin

sleep-independent circadian rhythms in the body

example: melatonin

completely unaffected by sleep deprivation

what type of variable (rhythm) persists in the constant routine?

body temperature, as it rises in the day and falls at night