Biological Rhythms Flashcards
What are the two main governors of biological rhythms
- Endogenous pacemakers: internal biological clock
2. Exogenous zeitgabers: changes in external environment
What are two examples of circadian rhythms
- Sleep/wake cycle
2. Core body temperature
Outline procedure of cave study
- Observed the effects of no natural light or clock
2. Two months in a cave in alps and then again for 6 months in Texas
What were Siffres findings
- Emerged from alps in mid September thinking it was mid August
- Free running biological rhythm settled at around 25 hours
Bunker study and what it shows
- A month in a bunker
- All went to 25 hour Sleep/wake
- Shows sleep wake around 25 but entrained by exogenous zeitgabers such as day and meal time
Study against role of exogenous zeitgabers
- 12 people, 3 weeks in cave
- Went to bed on time schedule
- Research’s sped clock to 22 hour
Cycle - Only 1/12 could adjust properly
- Show circadian rhythms are powerful
What are the two practical applications of circadian research
- Shift work and CVD
- When to take drugs
- Teenagers in school
Practical application to shift work
- Shown relationship between night shift and poor health
- 3 times more likely to develop CVD
- Due to stress of adjusting sleep/wake patterns and poor quality sleep during the day
- Cannot claim causal influence (could be these people have worse diet)
Practical application on drugs
- Circadian rhythms co-ordinate a number of body’s processes such as heart rate and hormone level
- Affects how well drugs are absorbed and distributed
- Led to development as to when to take medication for cancer or CVD (also anything)
3 mini a03
- Small samples (or individuals) not represtivtve of pop
2. Poor control: assumed artificial light had no affect but study showed S/W cycle can go from 22-28 using lights
Teenagers in school
- 2 hour later circadian rhythm than adults
- School disrupts this
- Research shown improved cognitive and emotional function
Describe the menstrual cycle
- An infradian rhythm governs by monthly changes in hormone oestrogen levels
- Between period and womb lining shred
- 28 days to complete
- Develops egg and womb lining growth thicker
Research into influence of exogenous factors
- 29 women with irregular periods
- Pheromones gathered from 9 other women each day of cycle via cotton pad
- Rubbed on upper lip
- Day one pads applied to all 20, day 2 next day, etc…
- 68% experienced changes that brought them close in sync with odour donor
Outline SAD
- Circannual rhythm but also circadian as distrust sleep
- Depressive symptoms in winter months
- Due to increased melatonin due to longer nights which disrupts serotonin levels
What are ultradian rhythms
- Stages of sleep that last 9 mins
2. Different brainwave activity monitored using EEG
Describe stages 1 and 2
- Light sleep
- Brain waves slow and become more rhythmic (alpha waves)
- Goes to delta waves as becomes deeper sleep
Describe stages 3 and 4
- Still delta
- Greater amplitude
- Deep sleep it slow wave sleep and is hard to wave someone
Describe stage 5
- Paralysis but brain active resembles awake brain
- REM
- Correlated with dreaming
Evolutionary basis of menstrual cycle
- Advantage to fall pregnant at same time so babies could be cared for collectively
- Validity of this has been questioned as if too many female were cycling together would increase competition highest quality males
- Could be both: evolution is not a design
Methodological issues in pheromone study
- Too many confounding variables such as diet and stress
- Changes are due to chance
- Small samples and self-report
- Other studies show no evidence for at all
Lab evidence for stages of sleep
- 9 participants in sleep lab with EEG
- Caffeine and alcohol controlled
- REM highly correlated with sleep
- Activity correlated with vividness of dream
- Replications confirm this and make up for small original sample
Describe the SCN
- Nerve cells above hypothalamus in each hem
2. Primary endogenous pacemaker in mammals, maintains circadian rhythm
How does the SCN receive info about light
- Optic nerve cross optic chiasm going to visual area
- SCN lies just above this and receives info this
- Even when eyes are closed so can adjust to changing patterns of daylight while asleep
Two animal studies and the CNS
- Destroyed 30 chipmunk SCN connections, retired to habitat and obervsed for 80 days
- Sleep/wake cycle disappeared and most were killed because awake at wrong time
- Mutant hamsters with 20 hour cycle bred and SCN placed in normal hamsters.
- Second group went to 20 hours
Both show importance of SCN in sleep wake cycle
How does the SCN control sleep/wake
- Relays daylight info to pineal gland
- During night secretes melatonin which induces sleep
- This is why causes SAD
Define exogenous zeitgabers
Sleep/wake a interaction of the two influences
Light as an exogenous zeightgeber
- Resets SCN
- Light detected by skin receptors: 15 p woken by light on back of knee
- Shows it’s a powerful EZ and does not need eyes to influence the brain
Social cues as EZ
- Babies sleep/wake random
- By 16 weeks babies are entrained by bedtimes and meal times
- Also adapting to local times for eat/sleeps is good for Jet lag
Multiple body clocks
- Pacemakers in many organs and cells
- Called peripheral oscillators and although influenced by, act independently of SCN
- Feeding patterns in mice could alter CR cells in liver by 12 hours while leaving SCN unaffected
- Suggests more complex aspects to Sleep/wake
What are body clocks found in liver and pancreas called
Peripheral oscillators
Problems with animal studies on sleep/wake
- Cannot generalise
2. Most are exposed to considerable harm
Influence of EZ overstated
- Blind man had to take sedatives to sleep and stimulants to stay in time with 24 hours, despite the usual social cues (under developed SCN probs to lack of stim)
- Arctic people have normal sleep/wake even when sun does not set
