Biological rhythms

Question 1

What is a biological rhythm?

Answer 1

Distinct patterns of changes in biological activity that conform to cyclical time periods.

Question 2

What are the 3 types of biological rhythms?

Answer 2

Circadian
Ultradian
Infradiun

Question 3

What is a circadian rhythm?

Answer 3

• 24 hour cycle

- e.g. sleep/wake cycle

Question 4

Who conducted a study into circadian rhythms?

Answer 4

Siffre

Question 5

What was Siffre’s study?

Answer 5

• Spent periods of time underground in caves with no access to natural light.
• His biological rhythm was just beyond 24 hours and he continued to fall asleep and wake up regularly.

Question 6

What was Aschoff and Wever’s study?

Answer 6

• Participants spent 4 weeks in a WW2 bunker deprived of natural light.
• All but 1 displayed a circadian rhythm of 24-25 hours.

Question 7

What do both Siffre’s and Aschoff and Wever’s study suggest about circadian rhythms?

Answer 7

Both studies suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24 hour day.

Question 8

State 2 positives of research into circadian rhythms.

Answer 8

Practical application of shift work:
- reduced concentration around 6 in the morning meaning mistakes are more likely to be made
- Knutsson - shift workers are 3x more likely to develop heart disease which may be partly down to the stress of adjusting to different sleep/wake cycles and the lack of quality sleep during the day
Practical application to drug treatment:
- led to development of guidelines to do with timing of drug dosing

Question 9

State 2 negatives of research into circadian rhythms.

Answer 9

Use of case studies and small samples:
- may not be representative
- lack generalisability
Poor control of variables:
- had access to artificial light

Question 10

What is an infradian rhythm?

Answer 10

Frequency of less than one cycle in 24 hours.

E.G. menstrual cycle and Seasonal Affective Disorder (SAD)

Question 11

Who conducted research into the menstrual cycle and exogenous factors?

Answer 11

Stern and McClintok

Question 12

What was Stern and McClintock’s study?

Answer 12

• 29 women with a history of irregular periods.
• Samples of pheromones were gathered from 9 women (cotton pad in their armpit).
• On day 1 pads from the start of the menstrual cycle were applied to all 20 women.
• On day 2 they were given a pad from the second day of the cycle etc.
• Found that 68% of women experienced changes to their cycle.

Question 13

What is SAD?

Answer 13

A depression associated with seasonal changes, usually the onset of winter and increased darkness.

Question 14

What is an ultradian rhythm?

Answer 14

Frequency of more than one cycle per 24 hours.

E.G. stages of sleep.

Question 15

What are the stages of sleep?

Answer 15

• Stage 1 and 2: light sleep in which the person is easily woken and brainwave patterns start to become slower and more rhythmic (alpha) and become even slower as sleep becomes deeper (beta).
• Stage 3 and 3: delta waves, deep sleep.
• Stage 5 and REM: body is paralysed yet brain activity speeds up and a person experiences REM (rapid eye movement).

Question 16

State 2 positives of research into ultradian and infradian rhythms.

Answer 16

Evolutionary basis for menstrual cycle:
- advantageous to fall pregnant at same time so new borns could be raised collectively
- increase chance of offspring surviving
Evidence supports stages of sleep:
- Dement and Kleitman
- monitored sleep patterns of 9 adults in a sleep lab with their brainwave activity recorded on an EEG
- researchers controlled effects of alcohol and caffeine
- REM activity during sleep was highly correlated with the experience of dreaming

Question 17

What is an endogenous pacemaker?

Answer 17

Internal body clocks that regulate many of our biological rhythms.

Question 18

What is the SCN?

Answer 18

• A tiny bundle of nerves located in the hypothalamus in each hemisphere of the brain.
• Primary endogenous pacemaker in mammals.
• The SCN receives information about light, even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we’re asleep.

Question 19

Who conducted an animal study on the SCN?

Answer 19

Decoursey

Question 20

What was Decoursey’s study?

Answer 20

• Destroyed the SCN connections in the brains of 30 chipmunks and then placed them back in their natural habitat and observed them for 80 days.
• Sleep/wake cycle disappeared.
• Significant number of the chipmunks had been killed by predators by the end of the study.

Question 21

What is an exogenous zeitgeber?

Answer 21

An external cue that may affect our biological rhythm.

Question 22

Name 2 exogenous zeitgebers.

Answer 22

Light:
- key zeitgeber than can reset the main endogenous pacemaker (SCN) and plays a role in the sleep/wake cycle
Social cues:
- schedules created by others
- e.g. human infants’ initial sleep/wake cycle is pretty much random
- at 6 weeks the circadian rhythms begin and by 16 week it is entrained

Question 23

State 3 negatives of research into exogenous zietgebers and endogenous pacemakers.

Answer 23

Ethics in animal studies:
- subject to considerable harm
- hard to generalise
Influence of exogenous zeitgebers may be overstated:
- Miles - studied young man who was blind since birth
- circadian rhythm was 24.9 hours and despite exposure to social cues his sleep/wake cycle could not be adjusted
- had to take sedatives at night and stimulants in the morning
- exogenous zietgebers had little bearing on circadian rhythms
Beyond the master clock:
- Damiola - feeding patterns in mice could alter circadian rhythms by up to 12 hours whilst leaving the SCN unaffected
- may be other complex influences on the sleep/wake cycle, aside from the master clock (SCN)