4.2.2 BIOLOGICAL RHYTHMS Flashcards
what are endogenous pacemakers?
the body’s internal ‘clocks’ that regulate many biological rhythms
what are exogenous zeitgebers?
external cues which may affect our biological rhythms
eg) the effect of light on the sleep/wake cycle
what are circadian rhythms?
- operate on a 24 hour cycle which is reset by levels of light
eg) sleep / wake cycle and core body temperature
- dictate when we should be awake and sleeping
what is the suprachiasmatic nucleus (SCN)?
- in the hypothalamus
- detects the level of light present and then uses this info to coordinate the activity of the entire circadian system
what is melatonin?
plays a role in ‘triggering’ sleep by responding to a decrease in the levels of light
what is an example of desynchronisation of circadian rhythms?
- jet lag
sleep rhythm dips at points in the day
when is it at it’s strongest?
what makes the dips less intense?
strongest sleep drive = 0200-0400 and 1300-1500
- if we have sufficient sleep the dips are less intense
the work of Siffre supports circadian rhythms
what was it and what does it suggest?
- in all of his studies, his free-running biological rhythm settled to 25 hours but this altered as he aged with the occasional 48-hour cycle
- only thing influencing him underground was his internal body clock
- left the cave in mid-September 1962 but through it was mid-August
- suggets the human body clock relies on exogenous zeitgebers to help it keep time
-> without these factors our body clock can extend, making us believe a day is longer than it is
what’s a limitation of the work of Siffre?
- it’s a case study
- cannot be generalised beyond the single participant
what is an infradian rhythm?
- rhythms that take longer than 24 hours
-> so there’s a frequency of less than one day - eg) menstrual cycle, Seasonal Affective Disorder
what is the menstrual cycle and how long is it typically?
- government by monthly changes in hormone levels which regulate ovulation
- cycle refers to time between first day of period, when the womb lining is shed - to the day before the next period
- typical cycle length = approximately 28 days (24-35 = normal)
what happens during the menstrual cycle?
- during cycle, rising levels of oestrogen cause ovary to develop and egg and release it (ovulation)
- after ovulation, progesterone helps womb lining grow thicker, readying the body for pregnancy
- if pregnancy doesn’t occur, the womb lining sheds (= period)
is the menstrual cycle endogenous or exogenous?
- an endogenous system
- but research shows it can be affected by exogenous factors
what did McClintock 1998 do?
- studied 29 women with history of irregular periods
- samples of pheromones were gathered from 9 of them at different stages in their menstrual cycle
-> via a cotton pad under their armpit - this was worn for 8 hours to ensure pheromones were picked up
- then treated with alcohol and frozen
-> + rubbed on the upper lip of other ppts
day 1
- cotton pads from start of cycle were applied to all 20 women
day two
- given a cotton pad from the 2nd day of the cycle
what did McClintok 1998 find?
found 68% of women experienced changes to their cycle which bought them closer to the cycle of their ‘odour donor’
- this was labelled as the MCCLINTOCK EFFECT
what is Seasonal Affective Disorder (SAD)?
- SAD is in the DSM-5 as a recognised mental disorder
- melatonin has been implicated in the cause of SAD
-> during nighttime, pineal gland secretes melatonin until dawn when there’s an increase in light - during winter, the light means the secretion continues for longer
- this is thought to then affect the production of serotonin
what are ultradian rhythms?
- biological rhythms that you have more than once a day
- biological rhythms that take less than 24hrs to complete, may often occur more than once over the course of a day
eg) stages of sleep
what are the 5 recognised stages of sleep?
- stages 1 and 2 are the sleep escalator
- stages 3 and 4 consist of the delta waves of deep sleep
- stage 5 is REM sleep, the stage in which dreaming occurs according to research
how long does each stage span for?
how many are completed?
what does each stage differ from the other in?
- 5 distinct stages that span 90 minutes
- you must complete multiple cycles throughout the night
- each stage has different brainwave activity linked to it
what happens in stage 1?
- light sleep
- muscle activity slows down
- occasional muscle twitching
- brainwave patterns are slower and more rhythmic (alpha + theta)
what happens in stage 2?
- breathing pattern and heart rate slows
- slight decrease in body temperature
what happens in stage 3?
- deep sleep begins
- brain begins to generate slow delta waves
-> (but they still have a greater amplitude than earlier wave patterns)
what happens in stage 4?
- very deep sleep
- rhythmic breathing
- limited muscle activity, brain produces delta waves
what happens in stage 5?
- Rapid Eye Movement (REM)
- brainwaves speed up and dreaming occurs
- muscles relax and heart rate increases
- breathing is rapid and shallow
- body is paralysed yet brain activity speeds up significantly in a way that resembles the awake brain (REM)
