Biopsychology - Endogenous Pacemakers and Exogenous Zeitgebers Flashcards
What is the role of the suprachiasmatic nucleus (SCN) in regulating biological rhythms?
The SCN is a tiny bundle of nerve cells in the hypothalamus, located in each hemisphere of the brain. It is crucial for maintaining circadian rhythms, including the sleep/wake cycle. The SCN receives information about light levels via the optic nerve, even when the eyes are closed, and adjusts the body’s clock accordingly.
What evidence from animal studies supports the role of the SCN?
DeCoursey et al. (2000): Destroyed the SCN in 30 chipmunks and observed them in their natural habitat for 80 days. The sleep/wake cycles disappeared, and many were killed by predators due to being active at night.
Ralph et al. (1990): Transplanted SCNs from mutant hamsters with a 20-hour cycle into normal hamsters, causing the recipients’ sleep/wake cycles to change to 20 hours.
How does the pineal gland and melatonin regulate the sleep/wake cycle?
The SCN sends signals to the pineal gland, which produces melatonin at night to induce sleep by inhibiting wakefulness. Melatonin levels drop during the day, helping maintain the sleep/wake cycle. Abnormal melatonin secretion is linked to Seasonal Affective Disorder (SAD).
What are exogenous zeitgebers and how do they influence biological rhythms?
Exogenous zeitgebers are external factors, such as light and social cues, that reset the biological clock. Light is the main zeitgeber and influences hormone secretion and blood circulation. Social cues, like meal and bedtimes, also help regulate sleep/wake patterns, especially in infants.
What research demonstrates the role of light as an exogenous zeitgeber?
Campbell and Murphy (1998) showed that light exposure to the back of participants’ knees could shift circadian rhythms by up to 3 hours. This indicates that light doesn’t need to enter the eyes to influence the SCN.
What is one evaluation point about the role of the SCN?
Research shows that other circadian rhythms are regulated by peripheral oscillators in organs like the liver and pancreas. Although these can function independently, the SCN still plays a key role in coordinating them.
What is one evaluation point about ethics in animal studies on the SCN?
Animal studies like DeCoursey et al. raise ethical concerns due to the harm caused to animals, such as increased vulnerability to predators. The justification for such research is debated.
What is one evaluation point about exogenous zeitgebers?
Laughton Miles et al. (1977) studied a young man blind from birth with a 24.9-hour sleep/wake cycle. Despite exposure to social cues, his rhythm couldn’t be adjusted, suggesting light is essential for biological rhythms
What is one evaluation point about methodological issues in zeitgeber research?
Findings from Campbell and Murphy’s (1998) study have not been replicated. Critics point out possible confounding variables, such as light exposure to other parts of the body.
