endogenous and exogenous pacemakers/ zeitgebers Flashcards
(11 cards)
What is the main endogenous pacemaker in mammals?
The suprachiasmatic nucleus (SCN), located in the hypothalamus, which helps regulate the sleep/wake cycle.
What evidence supports the role of the SCN in controlling circadian rhythms?
DeCoursey et al. (2000): Destroyed SCN connections in chipmunks; their sleep/wake cycle disappeared, and they were more vulnerable to predators.
Ralph et al. (1990): Bred mutant hamsters with 20-hour cycles; transplanting their SCN into normal hamsters caused the recipients to adopt the 20-hour rhythm.
What is the role of the pineal gland and melatonin?
The pineal gland releases melatonin in response to signals from the SCN. Melatonin induces sleep and is inhibited during wakefulness.
What are two limitations of SCN research?
May obscure other body clocks (peripheral oscillators).
Interactionist system – pacemakers and zeitgebers interact in real life; they cannot be studied in isolation.
: What are the ethical issues in animal studies of the SCN?
Studies like DeCoursey et al. exposed animals to harm, as many died after being returned to their natural habitat. Raises concerns over generalisability and welfare.
What are exogenous zeitgebers?
External cues that help regulate the sleep/wake cycle, such as light and social cues.
How does light act as a zeitgeber?
Light resets the SCN and regulates key functions such as hormone secretion and blood circulation. Studies show light can shift sleep/wake cycles by up to 3 hours.
How do social cues influence circadian rhythms?
Newborns’ sleep/wake cycles are random, but by 6 weeks, they begin aligning with adult-determined schedules. Social interaction helps entrain biological rhythms.
What is a limitation of using light as a zeitgeber?
Light has less influence in environments with extreme conditions (e.g., the Arctic). People can maintain regular rhythms despite minimal light variation.
What case study challenges the role of social cues?
Miles et al. (1977): A blind boy with a 24.9-hour rhythm couldn’t adjust to a normal 24-hour cycle, despite social cues—highlighting the dominance of endogenous pacemakers.
What does age-related insomnia research suggest
Older people have poorer sleep due to weaker circadian rhythms. However, changes in lifestyle (e.g. reduced stimulation) may also contribute.
