Note on Circadian Rhythm from Bowen University

1. CIRCADIAN RYTHMS
BY
BAMIDELE OLUBAYODE

2. INTRODUCTION
• Most organisms have evolved to coordinate their activities within
the day-night cycle caused mainly by the earth rotation rather
than simply responding to the day light transition.
• It would appear that such organisms have evolved real clocks to
the biological processes.
• The biological clock keeps record of the event that occurs once
in a day.Even in the absence of environment time cues, it
maintains a period close to 24 hours.

3. • The term Circadian comes from
two Latin words namely:
- “Circa” means around/about
- “diem/ dies” means day
• Circadian means “about a day”
source: Premnath

4. MEANING OF CIRCADIAN RHYTHM
• It is any biological process that displays an endogenous,
entrainable oscillation of about 24 hours. Although circadian
rhythms are endogenous (built-in, self sustained), they are
adjusted (entrained) to the local environment by external cues
called Zeitgebers, commonly the most important of which is
day light.
• Chronobiology is the study of circadian rhythms.

5. HISTORY OF CIRCADIAN RHYTHM
• The first written record was in the 4th century BC. Adrosthenes, a
scribe for Alexander the great, wrote that he observed on the
march to India that the leaves of the tamarind tree always opened
during the day and closed at night.
• The first recorded observation of an endogenous circadian rhythm
took place in 1729 by the French scientist Jean Jacques de
Mairan.
• In 1832 de Candolle discovered that the Mimosa opens it’s leaves
1-2 hours earlier each day

6. HISTORY OF CIRCADIAN RHYTHM CONT'D
• In 1896, Patrick and Gilbert observed that during a prolonged
period of sleep deprivation, sleepiness increase and decreases
with a period of about 24 hours.
• Simpson and Gailbraith in 1906 found daily temperature rhythms
in monkeys persist in constant darkness.
• In 1918, J.S Szymanski showed that animals are capable of
maintaining 24-hour activity pattern in the absence of external
cues.

7. HISTORY OF CIRCADIAN RHYTHM CONT'D
• In 1922, Richter shows persistent rhythms of activity in animals
(rats).
• Joseph Takahadi discovered the first mammalian “clock gene”
(clock) using a 24-hour biological rhythm controlled by a
“pacemaker”in the brain that sends messages to other systems in
the body.

8. BIOLOGICAL CLOCK
• Biological clocks are organisms'natural timing devices,
regulating the cycle of circadian rhythms.
• They are made up of specific molecules that interact with
cells throughout the body.
• Almost every tissue and organ contains biological clocks.
• Genes that make the clocks'molecular components have
been identified in humans, fruit flies, mice, plants and other
organisms.

9. MASTER CLOCK CONTROLLING CIRCADIAN RHYTHM
• A master clock in the brain coordinates all the biological
clocks in a living thing, keeping the clocks in synchrony.
• In vertebrates, the master clock is a group of approximately
20,000 nerve cells that form a structure called the
suprachiasmtic nucleus (SCN).
• The SCN is in a part of the brain called the hypothalamus and
receives direct input from the eyes.

10. IMPORTANCE OF CIRCADIAN RHYTHM
• It has been shown to regulate various aspects of :
- Metabolism
- Sleep-wake cycle
- Body temperature
- Behaviour in humans as well as other organisms
-Pattern of activity such as: eating habits and digestion
Hormonal secretion
Neurotransmitter secretion
In plants, circadian clock control processes such as leaves and
petals movement, closing of stomata & metabolic activities
associated with photosynthesis.

11. IMPORTANCE OF CIRCADIAN RHYTHM
• The photoperiodic system appears to depend on circadian clock
to measure the duration of the day and night, thus maintaining the
passages of the day and season.
• Arabidopsis thaliana a model species for plant genetics exhibits
visible circadian rhythm in the leaves movements and less
obvious rhythm in the expression of many genes.
• However, the daily rhythm of life is maintained by the circadian
clock.

12. ELEMENTS OF CIRCADIAN RHYTHM
• Circadian rhythms are believed to have three elements
1 The input pathway which relay environmental information to a
pacemaker.
2. The circadian pacemaker which is also called Oscillator that
generate the oscillation.
3. The output pathway through which the pacemaker regulates
various output rhythms.
• The input and output of the circadian system are specific to each
organism but the mechanism of the pacemaker appears to be
similar in all organisms.

13. CIRCADIAN RHYTHMS AND SLEEP PATTERNS
• Circadian rhythm has effect on the sleep patterns.
• The SCN controls the production of melatonin, a hormone that
causes sleepiness. It receives information about the incoming
light from the optic nerves which relay information from the eyes
to the brain.
• When there is less light - for example, at night - the SCN signals
the brain to make more melatonin to cause drownsiness.

14. MOLECULAR MECHANISM
• In 2017, researchers Jeffrey C. Hall, Michael Rosbash and
Michael W. Young won the prestigious Nobel Prize for their work
on molecular mechanism of circadian rhythms.
• They carried out the research on fruit flies which have a very
similar genetic make up to humans. In them, they isolated a gene
that helps control the body's clock.
• They demonstrated that the gene produces a protien that builds
up in cells overnight, then breaks down during the day.
• The process can affect sleep and brain functions.

15. FACTORS AFFECTING CIRCADIAN RHYTHM
• Changes in the body and environmental factors can
cause circadian rhythm and natural light- dark to be
out of sync.
- Mutations or change in certain genes can affect
biological clocks
- Jet lag or shift work causes changes in the light- dark
cycle.
- Light from electronic device at night can confuse
human biological clocks.

16. FACTORS AFFECTING CIRCADIAN RHYTHM
• Changes in the body and environmental factors can
cause circadian rhythm and natural light- dark to be
out of sync.
- Mutations or change in certain genes can affect
biological clocks
- Jet lag or shift work causes changes in the light- dark
cycle.
- Light from electronic device at night can confuse
human biological clocks.

17. EFFECT OF CHANGES IN CIRCADIAN RHYTHM
• Changes in the natural light- dark cycle can cause
sleep disorder which may lead to:
• Obesity
• Diabetes
• Depression
• Bipolar disorder
• Seasonal affective disorder

18. EFFECT OF CHANGES IN CIRCADIAN RHYTHM
• Changes in the natural light- dark cycle can cause
sleep disorder which may lead to:
• Obesity
• Diabetes
• Depression
• Bipolar disorder
• Seasonal affective disorder

19. CIRCADIAN RHYTHM AND JET LAG
• When you pass through different time zones, your
biological clock will be different from the local time.
• For instance, if you fly East from California to New York,
you lose 3 hours when you wake up at 7:00am on the
east coast, your biological clock is still running on West
coast time, so you feel the way you might at 4:00am.
• Your biological clock will reset, but it will do so at a
different rates. It often takes a few days for your
biological clock to align with a new time zone.
• Adjusting after gaining time may be slightly easier than
after losing time because the brain adjusts differently in

20. REFERENCES
• National Institute of General Medical Sciences:
Circadian Rhythm.
• www.slide share.net. circadian rhythm by Premnath
Ramachandranpillai.

21. REFERENCES
• National Institute of General Medical Sciences:
Circadian Rhythm.
• www.slide share.net. circadian rhythm by Premnath
Ramachandranpillai.

22. THANK YOU