✓ Infradian Rhythms & Ultradian Rhythms (AO1) Flashcards
What is an infradian rhythm?
an infradian rhythm is a biological rhythm that lasts longer than 24 hours, but less than a year
infradian rhythms can be weekly, monthly, or annually
What are two examples of infradian rhythms?
the menstrual cycle - last on avg. 28 days
seasonal affective disorder - circannual (yearly)
How does the menstrual cycle work?
levels of oestrogen cause the ovaries to develop an egg & release it (ovulation)
then progesterone causes the womb lining to thicken, ready for pregnancy
if pregnancy doesn’t occur, the egg is absorbed into the body & the womb lining leaves the body (menstrual flow)
What gland coordinates the hormones for the menstrual cycle?
the hormones are all coordinated by the pineal gland which may be influenced by light levels
(pineal gland & melatonin may modify the pituitary release of LH & FSH)
McClintock & Stern’s study?
10 year longitudinal study
29 women w a history of irregular periods
samples gathered from 9/29 then rubbed daily on the upper lip of the other 20 women
68% women’s cycles synchronised to the donor’s
What 2 studies support the menstrual cycle as an infradian rhythm?
McClintock & Stern
Reinberg
Reinberg’s study?
woman spent 3 months in a cave w dim light
menstrual cycle shortened to 25.7 days & took a year to return to normal once out of the cave
(supports EZ for the menstrual cycle)
What is Seasonal Affective Disorder?
diagnosed as a mental disorder in the DSM-5 manual
- form of depression w persistent low mood & lack of activity
- “winter blues” occurs in late autumn/winter
circannual rhythm (yearly)
What is the EZ & EP of SAD?
EZ (external cue)- shorter daylight hours in Winter
EP (internal clock) - pineal gland secretes melatonin at night so is active for longer
(increases sleepiness which lowers serotonin levels & leads to depression)
Which study supports SAD as an infradian rhythm?
Terman et al
Terman et al’s study?
Terman found that the rate of S.A.D is more common in New Hampshire (North US) w roughly 10% of ppl
vs.
only 2% of Florida (South US)
shows how light (EZ) affects S.A.D
What is an ultradian rhythm?
a rhythm in a cycle less than 24 hours
What is an example of an ultradian rhythm?
the sleep cycle
What are the features of the sleep cycle as an ultradian rhythm?
- typically lasts around 90 mins
- most will go through 4-5 cycles a night
- different stages w different levels of brainwave activity
- measured using EEGs
What is stage 1 of the sleep cycle?
- light sleep
- easily woken
- alpha brain waves (slow, rhythmic)
What is stage 2 of the sleep cycle?
- theta brain waves (even slower than alpha)
- sleep spindles (sudden bursts of activity)
What is stage 3 of the sleep cycle?
- delta brain waves (slower & sleeper hard to wake)
What is stage 4 of the sleep cycle?
- deepest stage of sleep
- growth hormones released
- sleep walking/talking
- (still delta)
What is stage 5 of the sleep cycle?
- R.E.M (rapid eye movement)
- body paralysed but brain activity speeds up as if awake
- dreams occur
