Biological Rhythms Flashcards
What is a biological rhythm?
A biological rhythm is an innate, biologically driven behaviour or process that is periodically repeated over a period of time.
Three Types of Biological Rhythm
Circadian - 24 hr cycle - eg sleep wake cycle
Ultradian - less than 24hrs - eg stages of sleep
Infradian - more than 24 hrs - eg menstrual cycle
Circadian Rhythms - sleep wake cycle
The Sleep-Wake cycle refers to our 24 hr daily sleep pattern consisting of approximately 16 hours of daytime wakefulness and 8 hours of night time sleep.
Circadian Rhythms - how does the body maintain a 24 hr sleep wake cycle - EP and EZ
Endogenous pacemakers (EP) - Control of biological rhythms is exerted from within - the suprachiasmatic nucleus in the hypothalamus is the main EP that controls other biological rhythms and information on light levels
Exogenous Zeitgebers (EZ) - Control is exerted from outside by environmental stimuli eg exposure to daylight
Circadian Rhythms Process using EP and EZ - A01
1 - lack of light (EZ) is detected by retina
2 - information is passed on to SCN (EP) in hypothalamus
3 - Pineal gland secretes melatonin and serotonin decreases
4 - Person goes to sleep
5 - The SCN stops secreting melatonin, serotonin increases
6 - Person awakens - repeats every 24 hrs
EVALUATION - (CIRCADIAN RHYTHMS) - Is the sleep wake cycle controlled by EP, EZ or both?
PEEL 1 - Reseach to support role of endogenous pacemakers - 30 chipmunks had SCN removed for 80 days and all chipmunks sleep cycle ceased - EP therefore responsible for keeping time to our circadian rhythm and ensures survival - however humans are apex predators so EP is less needed for survival
PEEL 2 - Research to show EP is important in the human circadian rhythm- Michael Siffre - went in a cave for 2 months where there was no light, no contact and so no EZ - found his circadian rhythm increased to 24.5 hrs - implies EP can hod humans to a 24 hr circadian rhythm without any EZ so biological clock is more important - however caver was used to being underground and was also wet and cold so can’t make assumptions
PEEL 3 - Real life application to role of EP - Eskimos in the arctic circle have daylight all summer and darkness all winter. They maintained a 24 hr circadian rhythm suggesting humans do not need EZ (Light) to regulate the rhythm - on the other hand they used black out curtains in the summer and UV light in the winter therefore stimulating EZ to help entrain the circadian rhythm to a 24 hr day
Ultradian Rhythms - why are the stages of sleep Ultradian
An Ultradian rhythm is a cycle that happens more than once every 24 hours. The sleep stages go from REM to NREM sleep every 90-100 minutes.
Ultradian Rhythms - explain the stages of sleep A01
Stage 1 - 4-5% - light sleep, muscle activity slows, occasional twitching
Stage 2 - 45-55% - breathing pattern and heart rate slows, slight decrease in body temp
Stage 3 - 4-6% - deep sleep begins, slow delta waves
Stage 4 - 12-15% - very deep sleep, rhythmic breathing, limited muscle activity, brain produces delta waves
REM - 20-25% - rapid eye movement , brain waves speed up and dreaming occurs, breathing is rapid and shallow as heart rate increases.
Ultradian Rhythms PEEL
Strength is there is research to support that Ultradian rhythms exist
Nine Participants ate normally then arrived at lab just before normal bedtime, they went to sleep with electrodes attached beside their eyes and on the scalp to measure brain activity and eye movements - they were woken by a doorbell various times in the night and asked to describe their dream if they were having one. PPTS frequently described dreams when woken in REM but rarely did in NREM sleep
Proves REM is the active stage and the body goes into these every 90-100 mins
However small sample size and some individual differences as well as environmental factors like mobile phone light.
Infradian Rhythms - how is the menstrual cycle an example of an Infradian rhythm
A period lasts longer than 24 hours, the menstrual cycle typically occurs over a 28 day period so it is therefore infradian
Infradian Rhythms - menstrual cycle AO1
1 - the hypothalamus stimulates pituitary gland to release LH and FSH
2 - LH and FSH stimulate the development of the follicle in the ovary
3 - As follicle develops, oestrogen is released, suppressing LH and FSH
4 - As oestrogen increases uterus lining - LH and FSH are restimulated
5 - This releases an egg causing progesterone to increase
6 - If ovum is not fertilised, progesterone and oestrogen decrease, the uterus lining sheds
Infradian rhythms - PEEL
One strength is that there is research to support that the menstrual cycle is affected by exogenous zeitgebers
McClintock and Stern conducted a study to see if there are external influences regulating the menstrual cycle. They got a number of women who were about to ovulate or had just ovulated to wear a pad under their arm to absorb sweat. These were given to other women to sniff . Their menstrual cycle was monitored and they found 68% of women experienced changes bringing them closer to the cycle of the donor
Therefore external factors like pheromones from other women can alter the Infradian rhythm hence EZ playing a part in infradian rhythms.
However confounding variables like diet and stress could have also affected changes in the women’s menstrual cycles.
