Biological Rhythms: Infradian Rhythms

Question 1

Infradian Rhythms

Answer 1

Less than one cycle in 24 hours

Question 2

Female Menstrual Cycle

Answer 2

• The human female menstrual cycle is about 28 days
• Rising levels of oestrogen cause the ovary to release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the womb for pregnancy. If pregnancy does not occur, the egg is absorbed and the womb lining comes away (menstrual flow)

Question 3

Stern And McClintock

Answer 3

• Studied 29 women with irregular periods. Pheromones were taken from some at different stages of their cycles, via a cotton pad under their armpits. These pads were cleaned with alcohol and later rubbed on the upper lips of the other participants.
• 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’.

Question 4

SAD

Answer 4

• Seasonal Affective Disorder (SAD) is a depressive disorder with a seasonal pattern (example of infradian rhythm)
• Symptoms are triggered during the winter months when the number of daylight hours becomes shorter

Question 5

Melatonin Production

Answer 5

• Low levels of light
• Melanopsin is a protein in the eye, sensitive to light
• Melanopsin carries signal to SCN
• SCN lies in the hypothalamus and is the endogenous pacemaker. Receives information about light levels from the optic nerves.
• Axon pathways to pineal gland
• Sends signal to the pineal gland, leads to an increase in the hormone melatonin at night, which helps t induce sleep
• Melatonin= induced sleep

Question 6

SAD Caused By Melatonin

Answer 6

• During the night, the pineal gland secretes melatonin until dawn when there is an increase in light
• In winter, less light means secretion goes on for longer.
• This has a knock-on effect on the production of serotonin in the brain (low serotonin is linked to depressive symptoms).

Question 7

A03 (Research On The Menstrual Cycle Show It’s Evolutionary Basis)

Answer 7

E- For our distant ancestors it may have been advantageous for females to menstruate together and become pregnant at the same time. In a social group, this would allow babies who had lost their mothers to have access to breast milk, thereby improving their chances of survival
E- This suggests that synchronisation is an adaptive strategy

Question 8

A03 (Methodology Used In Synchronisation Studies)

Answer 8

A03 (Methodology Used In Synchronisation Studies)

Question 9

A03 (Real-World Application)

Answer 9

E- Light therapy reduces the debilitating effects of SAD (e.g. excessive sleepiness) in around 80% of people. It is also safer than using antidepressants. However. Rohan et al. recorded a relapse rate of 46% over successive winters, compared to 27% in a comparison group receiving CBT.
E- This suggests that light therapy may be an effective short-term treatment but additional treatments may be required if benefits are to be maintained.