Circadian rhythms exhibit a period of about 24 h whereas circannual (seasonal) rhythms cycle over the course of a year. Both types of rhythms are coordinated by the brain's suprachiasmatic nucleus (SCN).

1. Dr. Manju Bhaskar
Assistant Professor
Department of Zoology
D. B. S. College (CSJM University)
Kanpur 208006
email: drmanjubhaskar19@gmail.com

3.  These are physical, mental, and behavioral
changes that follow a 24-hour cycle.
 These natural processes respond primarily
to light and dark and affect most living
things, including animals, plants, and
microbes.
 Chronobiology is the study of circadian
rhythms.
 One example of a light-related circadian
rhythm is sleeping at night and being awake
during the day.
 The Average Teen Circadian Cycle image
shows the circadian rhythm cycle of a typical
teen.

7.  Biological clocks are organisms’ natural timing devices,
regulating the cycle of circadian rhythms. They’re
composed of specific molecules (proteins) that interact
with cells throughout the body.
 Nearly every tissue and organ contains biological clocks.
 Researchers have identified similar genes in people, fruit
flies, mice, plants, fungi, and several other organisms that
make the clocks’molecular components.
 A master clock in the brain coordinates all the
biological clocks in a living thing, 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, orSCN.
 The SCN is in a part of the brain called the
hypothalamus and receives direct input from the
eyes.

8. DOES THE BODY MAKE AND KEEP ITS OWN
CIRCADIAN RHYTHMS?
 Yes,naturalfactorsin yourbodyproducecircadianrhythms.
 Forhumans,someof themostimportantgenes in thisprocessarethePeriodandCryptochromegenes.
 Thesegenes codeforproteinsthatbuildupin thecell’s nucleus atnight andlessen duringtheday.
 Studiesin fruitfliessuggestthattheseproteinshelp activatefeelings ofwakefulness,alertness,andsleepiness.
 However, signals from the environment also affect circadian rhythms. For instance, exposure to light at a different time of day can reset when the
bodyturnsonPeriodandCryptochromegenes.

9. • Hormonerelease
• Eatinghabitsanddigestion
• Bodytemperature
 However, mostpeoplenoticetheeffectofcircadianrhythmsontheirsleeppatterns.
 The SCN controls the production of melatonin, a hormone that makes you sleepy. It receives information about 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 tells the brain to make
moremelatoninsoyouget drowsy.

10. • Mutationsorchangesin certaingenes canaffectourbiologicalclocks.
• Jetlag orshiftworkcauseschangesin the light-darkcycle.
• Lightfromelectronicdevices atnight canconfuseourbiological clocks.
 These changes can cause sleep disorders, and may lead to other chronic health conditions, such as obesity, diabetes, depression, bipolar disorder,
andseasonalaffectivedisorder.

11.  Scientists learn about circadian rhythms by studying humans and by using organisms with similar biological clock
genes,such as fruitfliesand mice.
 Researchers doing these experiments control the subject’s environmentby alteringlightand dark periods.
 Then they lookfor changes ingene activityor othermolecular signals.
 Scientists also study organisms with irregular circadian rhythms to identify which genetic components of biological
clocks maybe broken.
 Understanding what makes biological clocks tick may lead to treatments for jet lag, sleep disorders, obesity, mental
healthdisorders, and otherhealth problems.
 Itcan also improveways forpeople toadjustto nighttimeshift work.
 Learning more about the genes responsible for circadian rhythms will also help us understand more about the human
body.

12.  Circadian rhythms are a core part of physiology.
 Disrupting the circadian system either behaviorally (jet lag or shift work, actual or simulated in a lab), or genetically (breaking
or altering the molecular clock), compromises the health and lifespan of a variety of organisms.
 In humans, when circadian rhythms are disrupted due to shift work or chronic jet lag, incompatible behavioral and
physiological events can coincide.
 Repeated disruption of biological rhythms by shift work and sleep disruption can lead to an increased risk for a wide variety
of diseases including heart disease, diabetes, cancer, obesity, depression, bipolar disorder, and sleep disorders .
 The circadian system is a core aspect of physiology and crucial for our health.
 Many studies have found that disrupting the circadian system increases the risk of disease, whereas supporting circadian
rhythms with consistent environmental input can support health.

13.  The term circannual rhythm is a derivative of the term circadian.
 Circadian rhythms are endogenously generated biological rhythms with a period length of
approximately one day (from the Latin circa diem).
 Correspondingly then, a circannual rhythm may be defined as annual.
 There are many different examples of circannual rhythms including the pupation rhythm in carpet
beetles, the urge to migrate in birds, hibernation cycles in ground squirrels, and cycles of reproductive
activity and moulting in ungulates.
 In species living outside of the equatorial zones, the seasonal change in the daily pattern of light/dark
exposure, (that is, the photoperiod), is the major synchronising signal for circannual rhythms.
 Responsiveness to photoperiodic changes ensures that appropriate physiological or behavioral
responses occur at the different phases of the sidereal year

15.  https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx
 https://link.springer.com/referenceworkentry/10.1007%2F978-3-540-29678-2_1057
 https://srbr.org/circadian-rhythms-what-they-are-and-why-they-matter/

16. Thank You