Lesson 13- endogenous pacemakers and exogenous zeigebers

Question 1

endogenous pacemakers

Answer 1

-bodys internal biological clocks
-suprachiasmatic nucleus (SCN), tiny cluster of nerve cells in hypothalamus, plays important role in generating circadian rhythms, acts as master clock linking other brain regions that control sleep and arousal, has control over other biological clocks throught body

Question 2

SCN

Answer 2

-neurons within scn synchronise with each other so that target neurons in sites elsewhere body receive time coordinated signals
peripheral clocks can maintain a circadian rhythm but not for very long, which is why they are controlled by scn
possible because of scn built in circadian rhythm which only needs resetting when external light levels change, receives info through optic nerve
regulates manufacture and secretion of melatonin in the pineal gland via the interconnecting neural pathway, sends signal to pineal gland directing it to increase production and secretion of melatonin at night and to decrease it as light levels increase in morning, melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness

Question 3

endogenous pacemakers evaluation

Answer 3

-Morgan 1995 bred strain of hamster that had abnormal circadiam rhythms of 20 hours, scn neurons from these hamsters were transferred to normal hamsters, started to display abnormal circadian rhythms of 20 hours, shows importance
-Folkard 1996 studied uni student Kate Aldcroft who spent 25 days in a lab, had no access to daylight or other exogenous zeitgebers that might have reset scn, at end of 25 days her core temperature rhythm was still 24 hours, shows importance
-many studies carried out on animals using unethical procedures, not ecologically valid as people do not have circadian rhythm tampered with in real world, physiological differences
-Folkard also found Kate’s sleep wake cycle had extended to 30 hours with periods of sleep as long as 16 hours, suggests exogenous zeitgebers may also be important in controlling cycle, may have more effect than endogenous

Question 4

exogenous zeitgebers

Answer 4

anything who origins are outside organism, envrionmental events that are responsbile for maintaining the biological clock of an organism
light and social cues

Question 5

light

Answer 5

-most important, receptors in the scn are sensitive to changes in light levels during day and use this info to synchronise activity of bodys organs and glands
-light resets internal biological clock each day, keeping it on a 24 hour cycle, a protein in the retina of the eye-melanopsin, sensitive to natural light critical in system
-when people move to night shift/different time zone, endogenous pacemakers try to impose their inbuilt rhythm of sleep (circadian rhythm), now out of synchrony with the exogenous zeitgeber of light, leads to disrupted sleep patterns, increased anxiety, decreased alterness and vigilance- jet lag

Question 6

social cues

Answer 6

-social stimuli such as meal times/activities may also have a role, Aschoff et al 1971 showed that individuals are able to compensate for the absence of natural light by responding to social cues instead
-circadian rhythms of blind people were thought to be no different than sighted people as both groups were exposed to the same social cues, sleep wake cycle of most blind people is still influenced by light during day because connections exist between eye and scn that dont involve necessity of sight
-human infants have pretty random sleep wake cycle, circadian rhythms begin at around 6 weeks and by 16 weeks most babies have some sort of cycle,due to parents imposing meal times and bed times, shows how control of exogenous zeitgebers can effect sleep wake cycle
-research suggests that adapting to local times for eating and sleeping rather than responding to natural feelings, is an effective way of entraining circadian rhythms and beating jet lag

Question 7

exogenous zeitgebers evaluation

Answer 7

-role of melanopsin in setting circadian rhythms comes from studies of blind people, Skene and Arendt 2007 estimate the vast majority of blind subjects who still have some light perception have normal circadian rhythms, suggests pathway from retinal cells containing melanopsin to scn is still intact, still important in blind peoples sleep wake cycle
-Burgess et al 2003 found exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival, important application
-Vetter et al 2011, compared sleep wake cycle and activity-rest patters of two groups of participants over 5 week period, one group remained in normal warm artificial light, the other experienced artificial blue light, all participants kept daily sleep log and wore devices which measured their movement, pps under warm light synchronised their circadian rhythm each day with the natural light of dawn, other group synchronised pattern to office hours, suggests shade and artificial/natural of light is important, cautious about findings