Endogenous pacemakers and exogenous zeitgebers Flashcards
sleep/wake cycle
a daily cycle of biological activity based on a 24 hour period (circadian rhythm) that is influenced by regular variations in the environment
└e.g. alteration of night and day
Endogenous pacemakers and the sleep/wake cycle
parts
The superchiasmatic nucleus (SCN)
Animal studies and the SCN
└Patricia DeCoursey et al (2000)
└Martin Ralph et al (1990)
The pineal gland and melatonin
Endogenous pacemakers
internal body clocks that regulate many of our biological rhythms
└e.g. influence of the superchiasmatic nucleus (SCN) on the sleep/wake cycle
The superchiasmatic nucleus (SCN)
└a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
└one of the primary endogenous pacemakers in mammals
└is influential in maintaining circadian rhythms e.g. sleep/wake cycle
└nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area
└located above the optic chiasm
└receives information about light directly from the optic chiasm
└continues even when closed
Animal studies and the SCN
list
└Patricia DeCoursey et al (2000)
└Martin Ralph et al (1990)
Animal studies and the SCN
Patricia DeCoursey et al (2000)
└destroyed the SCN connections in the brains of 30 chipmunks who were returned to their natural habitat and observed for 80 days
└sleep/wake cycle of chipmunks disappeared by the end of the study
└significant proportion killed by predators
└awake and vulnerable to attack when should have been asleep
Animal studies and the SCN
Martin Ralph et al (1990)
└bred mutant hamsters with 20 hour sleep/wake cycle
└when the SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, their cycles became 20 hours
└studies emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle
The pineal gland and melatonin
└the SCN passes information on day length and light that it receives to the pineal gland (located behind the hypothalamus)
└night: pineal gland increases production of melatonin
└chemical that induces sleep
└day: pineal gland inhibits production of melatonin
└melatonin has been suggested as a causal factor in seasonal affective disorder
Exogenous zeitgebers and the sleep/wake cycle
parts
Light
Social cues
Exogenous zeitgebers
external cues that may affect or entrain our biological rhythms
└e.g. influence of light on the sleep/wake cycle
└external factors in the environment that reset our biological clocks through a process known as entrainment
└zeitber= German for time giver
Exogenous zeitgebers and the sleep/wake cycle
Light
└key zeitgeber in humans
└can reset their bodies main endogenous pacemaker (SCN), thus maintains sleep/wake cycle
└indirect influence on hormone secretion and blood circulation
└Scott Campbell and Patricia Murphy (1998)
└light may be detected by skin receptor sites on the body even when the same information is not received by the eyes
└15 participants were woken up at various times and a light pad was shone at the back of their knees
└researchers managed to produce a deviation in the participants sleep/wake cycle of up to 3 hours
└suggests light us a powerful exogenous zeitgeber, doesn’t only rely on eyes to influence the brain
Exogenous zeitgebers and the sleep/wake cycle
Social cues
└human infants sleep/wake cycle initially ransom
└6 weeks- circadian rhythms begin
└16 weeks- most babies entrained
└key influence is most likely schedules set by adults
└mealtimes/bedtimes
└jetlag improved when adapting to local eating/sleeping times to entrain circadian rhythms
Endogenous pacemakers and exogenous zeitgebers
limitations
summary
Beyond the master clock (SCN)- Francesca Damiola et al (2000)
Ethics in animal studies - DeCoursey et al (2000)
Influence of exogenous zeitgebers may be overstated - Miles et al (1977)
Methodological issues in studies - Campbell and Murphy (1998)
Endogenous pacemakers and exogenous zeitgebers
limitations
Beyond the master clock (SCN)
└research suggests there are numerous circadian rhythms in many organs and cells in the body
└peripheral oscillators
└in adrenal gland, oesophagus, lungs, liver, pancreas, thymus and skin
└highly influenced by suprachiasmatic nucleus
└can act independently
└Francesca Damiola et al (2000)
└changing feeding pattern of mice
└could alter circadian rhythms of liver cells by up to 12 hours
└leaving rhythm of SCN unaffected
└suggests may be other complex influences on the sleep/wake cycle other than the SCN
Endogenous pacemakers and exogenous zeitgebers
limitations
Ethics in animal studies
└DeCoursey et al (2000)
└animals exposed to harm and risk when returned to their natural habitat
└debatable if what we learn from the studies justifies the unethical procedures
