Chronobiology

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Dr. Jayant Biswas
What are body rhythms?
• Body rhythms are biological processes that
show cyclical variation over time…ranging
from hours to years and reflect the influence
of the earths rotation upon us… it's living
inhabitants, along with plants and animals.
Glossary of Chronobiological Terms
•
Biological clock; a term implying an underlying/internal physiological
mechanism that gives a time sense to every living organisms i.e., when to eat,
sleep/awake etc.
•
Biological rhythm; a cyclical, repeated variation in a biological function.
•
Circadian rhythm; a cyclical variation in a metabolic , physiological or
behvioural process with a period of about 24h when in constant conditions (the
term ‘circadian’ is derived from the Latin circa meaning about and diem
meaning day).
– Ultraradian: Rhythms faster than 24 h
– Infradian: Rhythms slower than 24 h
•
Circaseptan rhythm; a cyclical variation in a metabolic, physiological or
behvioural process with a period of about a week when in constant conditions.
•
Circannual rhythm; a cyclical variation in a metabolic, physiological or
behvioural process with a period of about an year.
Glossary of Chronobiological Terms
•
Crepuscular activity; an activity mainly performed at dusk and/or dawn.
•
Critical photoperiod; that 24h LD ratio at which 50% of the population under
study is photoperiodically switched from one state to another, e.g. into flowering
from non-flowering, or into development from diapause.
•
Diapause; a period of arrested growth or reduced physiological activity,
commonly induced by a seasonal change in photoperiod (i.e. day-length); a term
used mainly for invertebrates, especially insects.
•
Diel rhythm; a rhythm that has been measured only in natural or artificial daynight cycles, and not yet known to persist in constant conditions – cf. circadian.
•
Diurnal activity; activity performed mainly during the daytime – cf. Nocturnal.
•
Dormancy; a term used either more or less synonymously with diapause, but
especially for plants.
Glossary of Chronobiological Terms
• Endogenous; of rhythms or other forms of biological timekeeping
controlled from within the organism by some kind of physiological
‘ biological clock ’.
• Entrainment; the synchronization of one biological rhythm to another or
to a zeitgeber cycle, e.g. circadian rhythm are often entrained to the lightdark cycle.
• Exogenous; of rhythms or other biological timekeeping that arise solely,
or mainly, as direct responses to environmental signals cf. Endogenous.
• Free-running; when biological rhythms run at their own ‘natural’
frequency in constant conditions, and which are therefore not entrained to
a zeitgeber such as a day-night cycle and so are only generated and
controlled by the biological clock.
• Hibernation; winter or cold season dormancy.
• Hour-glass; an interval-timer which does not oscillate (i.e. repeat its
timing cycle) in constant conditions.
Glossary of Chronobiological Terms
•
Melatonin; a hormone produced rhythmically in vertebrates by the pineal gland, a
pea sized organ at the center of the human brain.
•
Nocturnal activity; activity performed mainly at night – cf. Diurnal.
•
Oscillator; the internal and therefore unseen, or endogenous oscillator (the
biological clock ) that produces an overt measurable biological rhythm in the
organism.
•
Period; the length of one complete cycle of a rhythm.
•
Phase; a particular reference point in the cycle of a rhythm, e.g. the daily onset of
locomotor activity, or the light-to-dark transition in a zeitgeber cycle.
•
Phase-response curve (or PRC); the 24h profile of an organism’s phase shifts in
response to environmental signals.
•
Phase shift; a shift in a biological rhythm along its time axis so whilst the period
remains the same the time at which the rhythm occurs changes e.g. a rhythm
normally occuring at 2pm experiences a 2 hour phase shift and so then starts at
4pm instead. The term phase shift is also used to mean the resetting of a rhythm;
either as an advance shift (i.e.earlier ), or as a delay shift (i.e. later ) along the
rhythms time axis.
Glossary of Chronobiological Terms
•
Photoperiodism; the seasonal day-length responses that cause altered
physiological states such as flowering or non-flowering, diapause or development;
the photoperiod is usually taken as the time between lights-on and lights-out in an
artificial LD cycle (though many photoperiodic responses are in reality to changes
in night length) – see critical photoperiod .
•
Rhythm; a function which oscillates or cycles at a regular frequency. Biological
rhythms are the overt, measurable activities generated by some internal oscillator
(or ‘clock’).
•
Skeleton photoperiod; experimental photoperiod cycle consisting of one long
light phase followed by darkness interrupted by a short light break, with the
organism responding as if the interval between the first light-on and the second
light-off marked a single photophase.
•
•
Tau; The ‘natural’ period of a biological rhythm free-running in constant conditions.
Temperature coefficient.
•
Temperature compensation; In simple terms Biological Clocks are not effected
by different temperatures, whereas other physiological systems are.
Glossary of Chronobiological Terms
• Zeitgeber; from the German for meaning "time giver". A periodic
environmental signal that entrains some biological rhythm , for
example a natural or artificial day-night cycle for a circadian rhythm
( but may also be a temperature cycle, or social cycle).
• Zeitgedächtnis; from the German for ‘time-memory’. Used mainly in
reference to the time-sense in honey bees by which they can be
trained to come to feed at particular times of day.
Examples of Biological Rhythms
• Seasonal migrations
• Mating seasons
• Menstruation
• Circadian rhythms:
– Daily rhythms
Inherent Biological Rhythms
• Biosystems Rhythms
– second cycles (sec) - cardiac
– circadian (day) - sleep cycle - melatonin (pineal)
– circaseptan (week) - mitotic activity of human bone
marrow, balneology, bilirubin cycle neonatology
– circalunar cycles (month) - menstrual cycle
– annual (year) cycles - animal’s coats – weight loss &
gain by the season.
Zeitgebers: External Cues Help Set Circadian Rhythms
• Internal clocks interact with
zeitgebers.
• Light is an important human
zeitgeber.
• Human “free-running” cycle is
about 25 hours.
• Blind individuals and sailors
serving on submarines may
experience sleep problems.
Synchronizers
–stimulated by light, temperature social
interactions, barometric pressure etc. etc.
• Light information
transmitted to the
brain by non-visual
neurons originating
in the back of the
eye
The Suprachiasmatic Nucleus in the
Body’s Master Internal Clock
• “supra” – above (above optic
chiasm)
• SCN is near:
– Hypothalamus
– Flow of visual info
• Retinohypothalamic
pathway
– Axons from eyes going to
hypothalamus
– Provides light info to
hypothalamus to maintain
circadian rhythms
SCN Activity and Light/Dark Cycles
• The SCN is active during the day in both
diurnal and nocturnal animals.
• The SCN tells the animal whether it’s
day or night, but not how to behave.
• Transplants of SCN establish
rhythms in recipient animals.
donor
Single SCN explants generate a circadian rhythm
Reppert, S.M. & Weaver, D.R., Nature 418, 935 - 941 (2002)
How the Internal Clock works
• Oscillations of protein production and
degradation serves as the “ticking” of the
internal clock (takes about 24 hours).
• Light may participate in the triggering of
some of these protein fluctuations.
The Biochemistry of Circadian Rhythms
• Cortisol
– release is highest in the morning and
drops during the day.
• Glutamate
– Released by the retinohypothalamic
tract during light
• Melatonin
– released only at night (by the retina
and the pineal gland).
Is the biological clock really a clock?
A Comparison
• Wrist watch
• SCN (biological clock)
• Driven
with
a
predetermined period (nearly
24h)
• Driven by a genetic program
with
a
pre-determined
period (~24.1h)
• Has error
• Has error
• Able to re-set
• Able to re-set
• “Free will”
– We act in accordance or
defiance of the clock
• “Free will”
– We act in accordance or
defiance of the clock
• Can give to others
• Can give to others
Viewpoint Challenge
• Traditional view – biological rhythms are exogenous
• Blood pressure variation is interpreted as an activity
variation, thus external.
• Now, many claim that biological rhythms are endogenous
• Blood pressure variation is interpreted as a hormonal
variation, thus internal.
The consequences of disrupting Biological rhythms.
• When external cues change we have to re-adjust
our internal clock…….
SHIFT WORK
JET LAG
What is Shift Work?
• The term shift work is defined as an
arrangement of work hours that uses two or
more teams (shifts) of workers in order to
extend the hours of operation of the work
environment, beyond that of the conventional
office hours.
• Knutsson, 1989
Why population of shift workers increasing day by day?
• We need doctors, nurses, policeman, hotel staff
etc. as a part of our social life.
• Expensive machines and continuity in their
functioning in modern industries is extremely
mandatory and cost-effective.
• Quality in the current-day lifestyle demands
immediate and round-the-clock service from
various indispensable sectors.
Problems with shift Work
• Rising early or retiring to bed earlier than normal is an
example of phase advance.
• Going to bed late or getting up late is an example of phase
delay.
• By delaying/advancing our rhythms we are compromising
our ability to cope in the short term.
• On average it takes approx 3 days to adjust to a 12 hour
shift in time.
Exposure to Shift Work with Circadian Disruption Involves:
•
•
Internal & External Desynchronization
•
Sleep Deprivation with:
• Neuro- Endocrine Changes,
• Immune- Suppression.
Exposure to Light at Night (LAN,
“Light Toxicity”) with Suppression of
Melatonin
• Increased sleepiness: Poor sleep,
both qualitative and quantitative.
Major Problem: Performance decrement
• Besides several Psychosocial/ Psychophysiological/ Clinical
Problems, the most dangerous is the decrement in overall
performances of the Shift-workers.
Shift workers are more susceptible to
diminished performance and attention
deficits that considerably compromise
public health safety and productivity.
Safety declines over successive
night shifts (Folkard & Tucker 2003).
Major Accidents due to Negligency during Shift Work
In
the US $77billion annually as a
result of accidents and ongoing
medical expenses due to shift work
related illnesses.
• Tragedy
• Bhopal gas tragedy
Time
00.56 h
• Chernobyl nuclear disaster
01.23 h
• Three-mile Island incident
04.00 h
• Rhine chemical spillage
Early morning
• Gaisal train disaster
01.15 h
How can we lessen the impact/effects of shift work?
Chronotype
LARK Type
OWL Type
• Select the Morning type and Evening type of
people and distribute the shit accordingly
How can we lessen the impact/effects of shift work?
–Speed Rotation:
»
Fast Vs Slow
• Direction of Rotation:
•
Clockwise Vs. Anticlockwise
How can we lessen the impact/effects of shift work?
Clockwise rotation:
Quickly rotating shift system:
•Minimize
sleep
(Fischer et al., 1997)
deprivation
•Minimize
circadian
rhythm
disruption (Knauth 1993, 1995)
•
•Improve social contacts (Knauth
1993, 1995)
•Improve alertness and well-being
(Williamson & Sanderson 1986,
Phillips et al., 1991)
•Better tolerated by the
shift workers
•Improve production &
well-being (Czeisler et al.,
1982)
•Improve sleep quality
(Folkard 1993)
•Reduce physical, social
and
psychological
problems (Landén 1981)
JET LAG
Jet
Lag
only
occurs when flying
from East-West or
from West to East.
In
other words
when we change
time zones.
Jet Lag does
not occur form
North-South
and vice versa!!
Example
You fly from Scotland
–Boston (USA). You
leave at 11am arrive
5pm British time
actually it is 12pm in
Boston...by 8pm
Boston time you’ll be
tired as it is 1am to
you normally!!
JET LAG
• Its easier to adapt to jet lag when flying in a westerly
direction because the day of travel is lengthen,
whereas it is shortened when travelling east!
• As our endogenous cycle is about 25 hours we are
more able to cope with phase delay than phase
advance.
• We can stay up when we should be a sleep but we
don’t like being woken we want to sleep!
JET LAG
• Evidence
Schwartz et al (1995) found that east coast
US baseball teams did better when
travelling West (phase delay) than West
coast teams who travelled East (phase
advance). The time difference was 3 hours.
This would give the East coast an
advantage!!
Jet Lag…How can we lessen the impact/effects of Jet Lag?
• Use melatonin to reset the body
clock..
• Adopt local eating times etc to help
reset the biological clock as soon
as possible.
Application of chronobiology across the lifespan:Adolescence
•
15 year old student with difficulty waking up in the
morning, finds his best “study time” is between 9 pm
and 1 am and hasn’t gone to sleep before 2 am for the
past 4 weeks.
•
What is this? What can he do about it?
•
A 65 year old man retired from a career in finance
wants to watch the late show with his wife and sleep-in
now that he’s retired, but he feels compelled to sleep at
8:30 pm and is awake each morning at 4 am. Wife is
offended that he’s “avoiding” her at night.
•
What is this? What can he do about it?
Mental Tiredness
Sleeplessness
Insomnia
Sleeping Inertia
THANK YOU FOR YOUR
PATIENCE
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