3. What are biological rhythms?
• Normal biological fluctuation which occurs in an
organism in response to periodic, cyclic changes in
its internal environment. These fluctuations regularly
occur on the physiological and psychological level,
and they involve a change in energy level, hormonal
level, and sexual desire. Also called biorhythm-
internal rhythm
5. The role of endogenous
pacemakers and exogenous
zeitgebers in biological rhythms
6. Exogenous zeitgebers
• Exogenous zeitgebers are external cues or time-givers that help
to keep these rhythms in tune with the changing external
environment. If organisms were lacking these zeitgebers then
the biological rhythms such as the sleep wake cycle would, for
example, be on a different time frame to the external
environment in winter as decrease in daylight or the shorter
days would not be detected. Therefore exogenous zeitgebers
are crucial in keeping the biological rhythms in time with that of
the changing external environment. Some examples of
zeitgebers are sunlight, noise and social interaction
7. Endogenous pacemakers
• are internal ‘biological clocks’ that manage our rhythms. The main
pacemaker in mammals is the Suprachiasmatic Nucleus (SCN), a
cluster of nerve cells located in the hypothalamus. This detects
sunlight and alters our sleep- wake cycle when needed putting the
biological rhythm in time with the environment. This is the result of
the SCN stimulating the pineal gland to produce more melatonin
which induces sleep by inhibiting the mechanisms that create
wakefulness.
8. Ultradian Rhythms
• An ultradian rhythm is any biological process that
displays an endogenous entrainable oscillation of
less than 24 hours. When we use this term we are
referring to the 90-120 minute brain wave frequency
cycles that occur when we are both awake and
asleep. When we refer to an ‘ultradian’ in polyphasic
sleep we refer to the smallest amount of time
between the start of your last nap, and the start of
your next nap, in a schedule.
9. Circadian rhythm
• Often referred to as the "body clock," the circadian rhythm is the
24-hour cycle that tells our bodies when to sleep, rise, and eat—
regulating many physiological processes. This internal body clock
is affected by environmental cues, like sunlight and temperature,
and determines whether one feels wide-awake and energized or
tired and depleted at different times of the day
• e.g
• stomatal opening and closing.
• Birds singing in the morning
10. Infradian rhythms
• Infradian rhythms have a cycle of longer than one day.
Examples include the menstrual cycle and seasonal affective
disorder.
• The menstrual cycle lasts around 28 days, or one lunar month,
and has been the subject of psychological research due to the
behavioural changes that are often linked to the cycle, such as
increase in accidents, lower academic achievement, suicides
and crime (Dalton, 1964). Understanding biological rhythms
has changed PMS from being a psychological disorder to a
physiological event.
11. Circannual Rhythms
• Any biological rhythm involving a biological or psychological
process that occurs or fluctuates at intervals of approximately one
year, even in controlled environments from which seasonal cues
have been eliminated, such as the seasonal changes in behaviour
of some migratory birds, which persist even under constant
laboratory conditions from which fluctuations in temperature,
daylight, and other seasonal cues have been excluded.
12. Diurnal Rhythms
• In diurnality, the cycle of activities of an animal or a plant involves a 24-hour
period. The term diurnal describes an animal or a plant that is more active
during the day than at night. For instance, the plant whose flower opens
during the day is referred to as diurnal as opposed to nocturnal plant that
blooms at night. The timing is said to be associated with their pollinators.
Sunflowers, for instance, bloom at daytime to attract bees. In contrast, night-
blooming cereus plant blooms at night to attract the sphinx moths.
13. Jet lag is a circadian rhythm sleep disorder
• Jet lag is a circadian rhythm sleep disorder
• Jet lag occurs when you travel across multiple time zones and
have trouble adjusting to the new schedule. After traveling a long
distance by air, your circadian rhythms may still be aligned with
the previous time zone. Your body may expect to sleep when it is
daytime in the new time zone or be awake when you are
supposed to sleep
