SECTION: Biological Rhythms
TOPIC: Biopsychology
Biological rhythms are the changes in bodily processes or behaviour over a repeated period of time, they may occur more
than or less than once within 24 hours. All rhythms are governed by the bodies internal clock (endogenous pacemakers)
and external environment (exogenous zeitgebers.)
Circadian Rhythm: Subject to a 24-hour cycle.
Sleep/Wake Cycle
Humans often feel awake in the day and drowsy in the night. This can be due to exogenous zeitgebers such as light or
endogenous pacemakers such as the suprachiasmatic nucleus.
SCN – The SCN is in the hypothalamus, near the optic nerves, it is sensitive to light changes and its intensity. When it
detects light, it reduces the production of melatonin (sleep hormone,) and the opposite when there is no light.
Light – Works as an external clock, it helps the body to maintain homeostasis.
Social Cues – imposed by everyday life schedules (meals, habits, exercise.)
Siffre’s Cave Study:
1975 – Siffre wanted to understand if the circadian rhythm
could be maintained without external cues. He spent 6 PEEL STRENGTH
months in a cave with no natural light, clock or external Practical Application – provides understanding for
sound. consequences when they are distrupted. Night workers
He found his biological rhythms settled at around 25 hours may experience reduced concentration by 6am, poor
on a regular cycle. This suggests endogenous pacemaker health has also been related to shift work = real world
can allow the circadian rhythm to ‘free run’ but may be economic value (productivity.)
slightly governed by external cues.
PEEL WEAKNESS
PEEL STRENGTH Individual Differences – studies on the circadian rhythm
are small/individual case studies. Sleep/wake cycle can
Medical treatment – Research has improved medical vary from person to person, for example teenagers have
treatments; drugs can be administrated in a way to fit a a different cycle pattern due to hormone shifts.
person’s circadian rhythm. For example, aspirin has been Therefore, this idea may be meaningless if it can only be
found to be best at night due to bodily activity, research averaged and not applied to all.
can increase effectiveness of treatment.
Infradian Rhythm: Less than one cycle in 24 hours - infrequent
Menstrual Cycle
A 28-day cycle within females that is governed by hormone changes, regulating ovulation. Therefore, endogenous
pacemakers for the menstrual cycle are hormones.
Synchronising: Research has found the menstrual cycle can also be affected by external factors. McClintock studied 29
females, of which 9 gave samples of their pheromones. The females wore pads under their armpits containing these
pheromones for 8 hours per day. 68% of females found their menstrual cycle was changed to be closer to the ‘odur
donors’ cycle.
Seasonal affective disorder (SAD)
Another example of an infradian rhythm, of which a pattern of depression occurs during winter months. Many say it is due
the change in daylight hours.
TOPIC: Biopsychology
Biological rhythms are the changes in bodily processes or behaviour over a repeated period of time, they may occur more
than or less than once within 24 hours. All rhythms are governed by the bodies internal clock (endogenous pacemakers)
and external environment (exogenous zeitgebers.)
Circadian Rhythm: Subject to a 24-hour cycle.
Sleep/Wake Cycle
Humans often feel awake in the day and drowsy in the night. This can be due to exogenous zeitgebers such as light or
endogenous pacemakers such as the suprachiasmatic nucleus.
SCN – The SCN is in the hypothalamus, near the optic nerves, it is sensitive to light changes and its intensity. When it
detects light, it reduces the production of melatonin (sleep hormone,) and the opposite when there is no light.
Light – Works as an external clock, it helps the body to maintain homeostasis.
Social Cues – imposed by everyday life schedules (meals, habits, exercise.)
Siffre’s Cave Study:
1975 – Siffre wanted to understand if the circadian rhythm
could be maintained without external cues. He spent 6 PEEL STRENGTH
months in a cave with no natural light, clock or external Practical Application – provides understanding for
sound. consequences when they are distrupted. Night workers
He found his biological rhythms settled at around 25 hours may experience reduced concentration by 6am, poor
on a regular cycle. This suggests endogenous pacemaker health has also been related to shift work = real world
can allow the circadian rhythm to ‘free run’ but may be economic value (productivity.)
slightly governed by external cues.
PEEL WEAKNESS
PEEL STRENGTH Individual Differences – studies on the circadian rhythm
are small/individual case studies. Sleep/wake cycle can
Medical treatment – Research has improved medical vary from person to person, for example teenagers have
treatments; drugs can be administrated in a way to fit a a different cycle pattern due to hormone shifts.
person’s circadian rhythm. For example, aspirin has been Therefore, this idea may be meaningless if it can only be
found to be best at night due to bodily activity, research averaged and not applied to all.
can increase effectiveness of treatment.
Infradian Rhythm: Less than one cycle in 24 hours - infrequent
Menstrual Cycle
A 28-day cycle within females that is governed by hormone changes, regulating ovulation. Therefore, endogenous
pacemakers for the menstrual cycle are hormones.
Synchronising: Research has found the menstrual cycle can also be affected by external factors. McClintock studied 29
females, of which 9 gave samples of their pheromones. The females wore pads under their armpits containing these
pheromones for 8 hours per day. 68% of females found their menstrual cycle was changed to be closer to the ‘odur
donors’ cycle.
Seasonal affective disorder (SAD)
Another example of an infradian rhythm, of which a pattern of depression occurs during winter months. Many say it is due
the change in daylight hours.
