circadian rhythms

• example of circadian rhythm?

  sleep/wake cycle
• how long does one sleep/wake cycle last?

  24 hours
• how often does the sleep/wake cycle occur?

  daily
• sleep/wake cycle?

  • being awake during day (light) & sleeping at night (dark)
• what is the suprachiasmatic nucleus?

  • endogenous pacemaker
  • receives info about light
  • affected by external cues - light & dark
  • has own internal activity rhythm - persists even when isolated from rest of brain
• where is scn found?

  hypothalamus
• what is the pineal gland?

  • during night converts serotonin - melatonin
  • when melatonin released acts on brains sleeping mechanisms & makes you feel less alert & sleepy
• where is the pineal gland found?

  behind hypothalamus
• sleep/wake cycle in terms of endogenous pacemakers?

  1. low levels of light
  2. low levels of light detected by retina
  3. passes message onto scn
  4. this alerts pineal gland
  5. pineal gland converts serotonin into melatonin
  6. we start feeling drowsy & go to sleep
• who did research into endogenous pacemakers for sleep/wake cycle?

  decoursey et al 2000
• decoursey et al study?

  • destroyed scn connections in brain of 30 chipmunks
  • returned to natural habitat & observed for 80 days
  • regular sleep/wake cycle disappeared & by end many killed by predators as they were awake & vulnerable to attack
• what did decoursey et all study show?

  • how important scn is in establishing & maintaining circadian sleep/wake cycle
• name 2 exogenous zeitgebers that affect sleep/wake cycle?

  1. artificial light
  2. social cues
• artificial light affecting sleep/wake cycle?

  • stimulates scn & can dictate when we should be awake & asleep
  • can reset scn so can disrupt sleep/wake cycle
• social cues affecting sleep/wake cycle?

  • daily routines such as working hours & mealtimes influence cycle
  • time influences when we go to bed/feelings of tiredness
  • influence circadian rhythms as well as our internal biology
• what is the interactionist approach?

  • endogenous pacemakers & exogenous zeitgebers interact to ensure we are synchronised with outside world
  • circadian rhythms (sleep/wake cycle) capable of free runninh
  • means without influence of external cues scn will run to rhythm of 25 hours
  • regulated at 24 hours
• what is entrainment?

  • process of internal biological clock being adjusted by external cues
• function of endogenous pacemaker?

  • provides stable sleep/wake cycle
• function of exogenous zeitgebers?

  • provides mean for adjusting when environment changes
• define endogenous pacemakers?

  • internal mechanisms that affect the body
  • eg our biological clock
• define exogenous zeitgebers?

  • external cues that affect body
  • eg light/social cues
• 4 * of circadian rhythms?

  1. evidence to support role of scn by ralph
  2. evidence to support by siffre
  3. evidence to support by campbell & murphy
  4. practical application
• 3 X of circadian rhythms?

  1. use of case study in siffre
  2. use of animals in ralphs
  3. sample of campbell & murphy
• * evidence to support role of scn by ralph?

  • took scn from mutant breed of golden hamsters with c.r of 20 hours & transplanted it into hamster with normal 24hr rhythm
  • normal hamster showed shorter rhythm similar to hamster whose scn had received
  • shows lab based evidence for role of scn in controlling sleep/wake cycle
  • by manipulating hamsters scn sleep/wake cycle completely changed
• * evidence to support e.p regulates sleep/wake cycle by siffre?

  • cave explorer who spent 6 months in underground cave to deprive himself of natural light & sound
  • was completely cut off from e.z
  • after period of time cycle settled to 25 hrs not dissimilar from standard 24hr cycle in real world
  • shows real world evidence for role of scn in controlling sleep/wake cycle
  • even without environmental influences (light/social cues) was able to stick to rough 24 hr sleep/wake cycle
• * evidence to supprt role of e.z by campbell & murphy?

  • applied light to back of knees of 15 p - detected by receptors in skin
  • resulted in shift in p usual cycle of upto 3 hrs
  • suggests external cues can affect cycle
  • lab based experiment used artificial light to manipulate cycle by resetting scn & can also provide entrainment to change & shift b.r
• * practical application?

  • shift workers who do night shifts have period of reduced concentration at 6am - mistakes & accidents more likely to occur
  • advice of things to avoid (light) can be given so can sleep during day & be more productive at work on night shifts & less error prone
  • helpful to know as it means people who work night shifts can adjust behaviour so can minimise effects of sleep disruption
  • research is valuable for society
  • more productive & less error prone workforce good for economy
  • people getting more sleep so less likely to suffer negative health outcomes from poor sleep
• what is a biological rhythm?

  • pattern of change in body that occurs in cycles & repeats
  • can match daily, monthy, yearly cyclic changes in environment
  • different rhytms have cycles that last different amounts of time for them to complete & begin again