biological rhythms

Question 1

what are the three main biological rhythms?

Answer 1

circadian.
infradian.
ultradian.

Question 2

define circadian rhythm.

Answer 2

rhythms that occur ONCE over approximately 24 hours.

Question 3

define infradian rhythm.

Answer 3

rhythms that take LONGER than 24 hours to complete.

Question 4

define ultradian rhythm.

Answer 4

rhythms that happen MORE THAN ONCE in 24 hours - shorter than a day.

Question 5

which rhythm occurs once over approximately 24 hours?

Answer 5

circadian.

Question 6

which rhythm takes more than 24 hours to complete?

Answer 6

infradian.

Question 7

which rhythm happens more than once over 24 hours?

Answer 7

ultradian.

Question 8

define exogenous zeitgeber.

Answer 8

external time giver - environmental time cues.

Question 9

define endogenous pacemaker.

Answer 9

internal biological clock.

Question 10

what is the suprachiasmatic nucleus?

Answer 10

group of neurones in the hypothalamus that regulates the sleep/wake cycle.

Question 11

what is the pineal gland?

Answer 11

gland that releases melatonin to induce sleep.

Question 12

define nocturnal.

Answer 12

active at night.

Question 13

define diurnal.

Answer 13

active during the day.

Question 14

what is a biological rhythm? give an example.

Answer 14

natural event that occurs on a regular basis, cyclically.
e.g. the menstrual cycle.

Question 15

how are biological rhythms controlled?

Answer 15

controlled and reset by environmental factors called exogenous zeitgebers - e.g. light and temperature.
regulated by the body’s internal clock, known as endogenous pacemakers.

Question 16

what is an example of a circadian rhythm?

Answer 16

sleep/wake cycle.

Question 17

how is the sleep/wake cycle controlled?

Answer 17

exogenous zeitgeber = light.
endogenous pacemaker = SCN.
EXZ and ENP interact - light resets SCN.

Question 18

outline the six steps of the sleep/wake cycle.

Answer 18

1. light comes through eyelids.
2. photosensitive receptors in eye transfer info as an electric impulse.
3. optic nerve transmits information to SCN.
4. SCN is the main endogenous pacemaker for the sleep/wake cycle. sends message to the pineal gland.
5. pineal gland controls melatonin production.
6. melatonin prohibited, and we wake up.

Question 19

what is the name of the key study into the sleep/wake cycle.

Answer 19

Siffre (1962) - The cave study.

Question 20

Outline the procedure of Siffre (1962).

Answer 20

Siffre spent two months living in total isolation in a subterranean cave, without access to technology, clock, calendar or the sun.
he slept and ate when his body told him to do so, his goal was to discover how the natural rhythms of human life would be affected by living beyond time.
repeated it again a decade later - 6 months in a Texan cave.

Question 21

outline the findings of Siffre (1962).

Answer 21

on both occasions, he settled into a sleep/wake cycle of 25-30 hours, just beyond the usual 24 hour cycle.
on his final stay in 1999, he found his body clock went more slowly than when he was younger, stretching as far as 48 hours.
this supports the assumption that endogenous pacemakers exert an influence on circadian rhythms.

Question 22

outline two problems with Siffre’s study.

Answer 22

population validity - the research was a case study with only one ptp, so internal validity is low. even when he redid in 1999, his results differed. even when its the same person, there are factors which may vary that can prevent conclusions being drawn. cannot necessarily be generalised to the wider population.

controls - Siffre had access to artificial light that may have affected his sleep/wake rhythms. Czeisler showed that you can use dim light to adjust ptps circadian rhythm from 22 to 28 hours, meaning Siffre’s lamp may have been a confounding variable, thus limiting its validity. limits the support it can provide the influence of endogenous zeitgebers.

Question 23

discuss research that questions the influence of exogenous zeitgebers.

Answer 23

Folkard et al (1985).
isolated 12 ptps from natural light for 3 weeks in a dark cave, and manipulated clocks so that only 22 hours passed in a day.
none of the ptps could adjust comfortably to the pace of the clock, showing the strength of the circadian rhythm as a free running cycle, questioning the extent to which it can be overridden by exogenous zeitgebers.

Question 24

outline practical applications of research into circadian rhythms.

Answer 24

application to shift work.
knowledge of circadian troughs and desynchronisation has helped inform workplaces of how to avoid accidents caused by these (e.g. Chernobyl).

has also helped to reduce stress caused by nightshifts that lead to heart disease by recommending fixed shifts instead of rotating, or phase delay rather than phase advance when shifts do have to rotate.

Question 25

discuss individual differences as a limitation of circadian rhythms.

Answer 25

Czeisler (1999) found that individuals sleep/wake cycles can vary, sometimes from between 13 and 65 hours.
Duffy (2001) also identified that some people prefer to get up earlier (larks) and some prefer to go to bed later (owls).
also age differences in sleep/wake cycles (Siffre found as he got older his rhythm lengthened from 25 hours to 48 hours).

Question 26

give three examples of an infradian rhythm.

Answer 26

menstrual cycle.
hibernation.
seasonal affective disorder.

Question 27

outline the process of the menstrual cycle.

Answer 27

starts with the first day of a period, where the womb sheds its lining, and ends the day before the next period.
typically takes 28 days to complete.
rising oestrogen levels causes ovary to release an egg (ovulation). then progesterone causes the womb lining to grow thicker, readying body for pregnancy.
if pregnancy doesn’t occur, womb lining is discarded (menstruation).

Question 28

name a study that supports menstrual entrainment.

Answer 28

McClintock’s sweaty lip ladies.

Question 29

outline a study that shows the menstrual cycle may be influenced by exogenous factors.

Answer 29

although the menstrual cycle is an endogenous system, evidence suggests it may be influenced by exogenous factors, like the cycles of other women.
McClintock (1998) involved 29 women with a history of irregular periods.
gathered armpit sweat with pheromones from 9 of the women.
pads containing sweat were then rubbed on the upper lip of the other women.
68% of women experienced changes to cycle that brought them more in line with the cycle of their ‘odour donor’.
entrainment occurred - supports influence of exogenous factors.

Question 30

discuss evolutionary value as a strength of menstrual synchrony.

Answer 30

menstrual synchrony through entrainment thought to have evolutionary value.
advantageous to fall pregnant at the same time because new-borns could be cared for collectively (e.g. breastfeeding) and therefore more likely to survive.
however, the validity of this has been questioned (Schank, 2004).
ovulating at the same time could mean competing for best partner and their resources, so avoiding synchrony would be the more adaptive evolutionary strategy and therefore naturally selected.

Question 31

Discuss problems with synchronisation studies.

Answer 31

confounding variables - many factors may change cycles e.g. stress, diet, exercise, so changes observed may have occurred by chance.
small samples and reliance on self-report on own cycle.
failure to replicate - other researchers have failed to find any evidence of menstrual synchrony in all female samples.

Question 32

outline seasonal affective disorder.

Answer 32

symptoms of depression experienced with a seasonal pattern of onset ‘winter blues’.
circannual rhythm - yearly.
attributed to longer hours of darkness during winter.
melatonin secreted for longer as night is longer. this affects production of serotonin, causing onset depressive symptoms.

Question 33

give an example of an ultradian rhythm.

Answer 33

stages of sleep.
five stages.
one cycle takes approx. 90 minutes.
control of the cycle involves a network of centres in the brain communicating through a variety of neurotransmitters - key elements are the SCN and pineal gland.

Question 34

outline the 5 stages of sleep.

Answer 34

1 - light sleep, muscle activity slows down.
2 - breathing pattern and heart rate slows. slight decrease in body temp.
3 - deep sleep begins. brain generates delta waves.
4 - very deep sleep, rhythmic breathing. limited muscle activity.
5. rapid eye movement, brainwaves speed up and dreaming occurs. muscles relax and heart rate increases. breathing is rapid and shallow.

Question 35

outline evidence that supports distinct stages of sleep.

Answer 35

Dement and Kleitman (1957).
monitored brainwave activity of 9 ptps using EEG.
REM activity highly correlated with dreaming.
replications have found similar findings - REM is an important component in ultradian sleep cycle.