The biological clock controls periodic functions in living organisms like sleep cycles and photosynthesis. The suprachiasmatic nucleus acts as the master clock in the brain, keeping other biological clocks in sync and resetting them daily in response to light, temperature, and other cues. Circadian rhythms occur over 24 hours, like sleep-wake cycles, while circannual rhythms repeat yearly like bird migration. Lunar and tidal rhythms are influenced by the moon's phases. Photoperiodism refers to behavioral responses to changes in daily light/dark cycles and influences plant flowering and animal reproduction. Disruptions to biological clocks can cause disorders like jet lag.

1. ANIMAL PHYSIOLOGY
SEMINAR PRESENTATION
BY
U.ID

2. ON:
“THE BIOLOGICAL CLOCK”

3. POINTS COVERED….
#BASIC CONCEPT OF BIOLOGICAL
CLOCK
*CIRCADIAN RHYTHMS
=LUNAR & TIDAL RHYTHM
=CIRCA ANNUAL RHYTHM
#PHOTOPERIODISM

4. BIOLOGICAL CLOCK….(a life clock )
DEF:
an innate timing mechanism in living organism that
controls the periodicity of various functions or activities, such as
metabolic changes, sleep cycles, or photosynthesis etc,is termed as
BIOLOGICAL CLOCK.
= The study related to biological clock and its regulation is compiled in a
branch of science called as CHRONOBIOLOGY..
which simply means chrono-time & biology-study of life.

5. What is the master clock?
A master clock in the brain coordinates all the
biological clocks in a living body , keeping the clocks in
sync.
In vertebrate animals, including humans, the master
clock is a group of about 20,000 nerve cells (neurons) that
form a structure called the suprachiasmatic nucleus, or
SCN. The SCN is located in a part of the brain called the
hypothalamus and receives direct input from the eyes.

6. Physiology of biological clocks
#In mammals, cells for biological clock are located in the hypothalamus, in two clusters of nerve cells
called the suprachiasmatic nuclei (SCN).
#Light receptors in the retina are connected by nerves to the SCN.
#SCN & mammalian pineal gland are linked.
#Thus, light is detected by eye, which passes this information on to the SCN, which in turn passes the
information on to the pineal gland, controlling melatonin production.
* (, a hormone that is produced by the pineal gland in animals and regulates sleep and
wakefulness which is produced in high levels at night and low levels during the day)

7. #As SCN generates a rhythm that lasts longer than 24
hours, it needs to be reset each day.
- Reset or adjusted by a number of factors called phase setters or
synchronizers or daily clues
light, darkness, temperature ,sound ,feeding time,etc.
EX: a nocturnal animal uses darkness for resetting its biological
clock and a diurnal animal uses light for resetting its biological clock
…

8. #It is an automatic clock which is
capable of producing biological
rhythms in both plants and animals…
……..rhythms ???......

9. BIOLOGICAL RHYTHMS-(periodic physiological fluctuation)
a sequence of bodily activities that repeat themselves through
time in the same order & at the same interval.
-These activities are cyclic in nature and are repeating at
regular intervals.
-Such as sleeping & awakening ,menstrual cycle, breeding
behaviour ,migration in birds are some good examples of
biological rhythms..

10. FORMS:…
ENDOGENOUS
(biological clock
control
EXOGENOUS
(direct control)
Endogenous Biological Rhythms
are naturally occurring cycles within our
bodies. They are 'built in' and naturally
occurs within our body. Endogenous
biological rhythms are regulated by the
organism and are not dependent on
external stimuli. Examples: are
circadian rhythms, body temperature
regulation, menstrual cycle, etc
Exogenous biological rhythms are
driven directly by the environment or
another external influence. Another
term for this type of biological rhythm is
a direct effect. An example of an
exogenous biological rhythm is the
hopping of sparrows on a perch when
a light is turned on. Such rhythms are
said to have a geophysical
counterpart; in this case, the presence
of light.

11. TYPES OF BIOLOGICAL RHYTHM…
CIRCADIAN
RHYTHM
CIRCANNUAL
RHYTHM
LUNAR &
TIDAL
RHYTHM

12. CIRCADIAN RHYTHM….
These are the daily biological rhythm which occurs on a 24hr
cycle ,and co-relates to the dark(night)-light(day)cycle .
The common physiologies under circadian rhythm are…
*the sleeping & awakening in humans
*flowering in lily and jasmine
*laying of eggs in hen..etc

13. Physically, the circadian clock is located in the suprachiasmatic nucleus (SCN) in
the hypothalamus of the brain.
{ The SCN is a tiny pinhead-sized area, containing just 20,000 or so very
small neurons, but it has the responsibility for sending signals to several
other parts of the brain to regulate the daily sleep-wake cycle, body
temperature, hormone production and other functions
The sleeping & awakening in humans

15. PHYSIOLOGY:
Exposure to natural daylight -stimulates a
nerve pathway from special
photoreceptive ganglion cells in the retina of
the eye.
- These cells contain a unique light-
sensitive pigment called melanopsin , and are
most sensitive to short wavelength “blue
light”.
- The light-dark signals are sent via the optic
nerve to the suprachiasmatic nucleus, which
uses them to reset its own circadian
clock each day.

17. LUNAR & TIDAL RHYTHM
The cyclical activities exhibited by organisms in relation to the
29day lunar month are called as lunar rhythms…
-Most obvious environmental variables affected by
the moon(lunar) are light and tide, and of these the tide
appears to have the greatest impact.
For this reason lunar rhythms seem to occur mostly in
marine species.
-During full moon and new moon days= tides are greatest
are called spring tides, caused by the cooperative
gravitational attractions of sun and the moon.
-At the moons’s quarters ,the sun and moon oppose each
other resulting in smallest tides called ebb tides.
-The spring and ebb tides occurs at an interval of
14.5days.Hence this rhythm has a duration of 29dys.

18. Certain animals’s activities are adapted to lunar cycles and they
exhibits lunar rhythms .
The best studied lunar.R are the monthly reproductive rhythms of
#palolo worms #fire worms
#sea lily
#may fly swarming
The breeding rhythms of these animals are
in relation to the phases of moon.
Example:
classical ex palolo worm(leodice),
-a tube dweller in coral reefs,its west indian species leodice fucata
- spawns only during 3rd quarter of june-july moon.
-The anterior part remains in its burrow beneath sea ,but the posterior ends
distended with ripe gamets ,break off and wriggle to surface in such wast number
that water is milky for an hr or two with the eggs and sperms.
,this swarming occurs at dawn.

19. The palolo worm,-exhibits a mixed rhythm, mixed between annual and
lunar.

20. CIRCANNUAL RHYTHM (circa- approximately , annual-yearly)
The biological activities exhibited by organisms repeated year by year
is termed as circannul rhythm.
There are certain physiological events occuring in many organisms with
an interval of 1yr or 365.
Example, migratory birds.
Every year they fly, without fail. Experiments have been carried out in
which the birds have been kept in a controlled environment, without the
chance of a disease or any situation that might cause them to migrate. But
still, the birds showed migratory behavior at the same time as they did
every year.
*Then there is the breeding cycles of different organisms. They
repeat the same cycle every year, at the same time.
*Another example could be the the hibernation cycle.
It is repeated even if the conditions do not require
hibernation.

21. Types of biological rhythm disorders?
Disorders may develop when natural biological rhythms are disturbed.
These disorders include:
sleep disorders: The body is “wired” to sleep at night. Disruptions in the
body’s natural rhythms can lead to affected sleep, including insomnia.
jet lag: A disruption in circadian rhythms when traveling across time zones or
overnight.
shift work disorders: When a person works outside the typical work day it
causes changes in typical circadian rhythms.
- excessive sleepiness affecting people whose work hours overlap with
the typical sleep period.

22. Photoperiodism (photos-light ,periods-length of time)
It is the functional or behavioral response of an organism to changes of
duration in daily, seasonal, or yearly cycles of light and darkness.
……….It occurs in both plants and animals as well……
The response of plants to the photoperiod(period of time each day during
which an organism receives illumination) expressed in the form of flowering is
called as photoperiodism….
When stimulated by light, an animal’s pituitary gland will release
hormones that affect reproduction. Thus, mating season of a species can be
made to occur at an unusual time by manipulating daylight. ------Long periods
of light followed by short periods = induce mating behaviour in species that
normally breed in autumn
(e.g., goats and sheep),
-while spring breeders (e.g., mink)
will start the reproductive process when daylight is increased.

23. Application of photoperiodism is common in the poultry industry, as daylight
affects egg-laying, mating.
*Reproduction in many species occurs at specific times of the year.
Plants produce pollen at the times of year when pollinators will be
active,
*while animals often reproduce in the spring and summer to take
advantage of the warmer temperatures.
*Often reproduction is triggered by a critical photoperiod.
•In many male animals, testis size is affected by photoperiod.
•In both hamsters and some birds for example the testes are small
in short days (i.e. in winter) but grow dramatically in long days.