1. AQA BioPsychology 4.2.2
Biological rhythms

2. Recap - Key Concepts
Biological rhythms: regular variations in the biological activity of living organisms, such as sleep, body temperature, alertness, neurotransmitter levels, etc.
Endogenous pacemakers: Biological ‘clocks’ in the brain controlling biological rhythms. Most likely the suprachiasmatic nucleus in the hypothalamus
Exogenous Zeitgebers (Timegivers): External stimuli that help towards regulating biological rhythms to the outside world
Circadian rhythms: 24 hrs periodicity
Ultradian rhythms: less than 24 hrs periodicity
Infradian rhythms: more than 24hrs periodicity

3. Infradian rhythms
Occurring to a period more than 24 hrs, such as the human menstrual cycle
Some of them may take place on a yearly basis and they are known as circannual rhythms, such as the migration of birds, and hibernation in squirrels bears, and hedgehogs
5 mins for 5 things - List details that you remember from the menstrual cycle from GCSE Biology

4. Menstruation (likely to happen every 28 days).
In a matter of months it gets established in the woman’s cycle.
Menstruation is also influenced by environmental events.
The synchronisation of menstrual periods attributes to the hypothesis of the unconscious detection of chemical scents called pheromones (relating to the physiology or the attraction of other species of the same or different sex) secreted at certain times during the menstrual cycle (Sabbagh & Barnard, 1984; Russell et al., 1980)

5. Mechanisms of menstration
The pituitary gland governs the phases of the menstrual cycle by influencing changes in the endometrium (the walls of the uterus) and the preparation of the ovum
Timonen et al., (1964) showed that during lighter months conceptions increased, whereas not during darker months

6. Exogenous zeitgebers and menstruation
Menstruation in the absence of Zeitgebers: It has been observed that menstruation starts mainly in winter (for the first time), and that because the pineal gland is affected by the melatonin’s secretion and the reproduction system in general (conceptions in lighter months) (Reinberg, 1967)

7. Seasonal affective disorder (SAD):
Seasonal affective disorder (SAD): Seasonal changes in behaviour can also be found in human beings. Individuals feel depressed during winter, and elated during summer. One suggestion is that absence of light increases melatonin, and what is suggested is light therapy (Rosenzweig et al., 1999). As an example, depression is mostly seen in northern than southern countries instead

8. Questions to consider
In 100 words outline what we mean by ‘endogenous pacemaker’
What is the name given to external events that play a role in rhythmic activities? Give an example
Discuss the association between SAD and exogenous zeitgebers?
Evaluate the research in biological rhythms