biopsych - y13 - endogenous pacemakers/exogenous zeitgebers Flashcards
what is an endogenous pacemaker?
internal body clocks that regulate many of our biological rhythms.
where is the suprachiasmatic nucleus located in the brain?
on top of the optic-chiasm.
what is an exogenous zeitgeber?
the external cues which may affect or entrain our biological rhythms such as the influence of light.
what is the sleep/wake cycle?
a daily cycle of biological activity based on a 24-hour period that is influenced by regular variations in the environment, such as alternation of light therapy.
what is the suprachiasmatic nucleus?
a tiny bundle of nerve cells in the hypothalamus in each hemisphere.
how does the suprachiasmatic nucleus work?
-the scn receives information about light levels from the optic nerve, which sets the circadian rhythm so that it is in synch with the outside world.
-it also sends signals to the pineal gland, which leads to the increase in the production of melatonin at night, helping to induce sleep, they work together as endogenous pacemakers.
-however, their activity is responsive ti the external cues of light.
how is light sent to the suprachiasmatic nucleus?
nerve fibres connected to the eye, cross in the optic chiasm which leads to the visual cortex.
-the scn receives information about light from the optic chiasm, even when our eyes are shut, allowing the biological clock to adjust to changing light patterns of daylight even when asleep (as eyelids are thin)
DeCoursey et al (2000)
-destroyed the SCN in 30 chipmunks who were then returned to their natural habitat and observed for 80 days
-their sleep/wake cycle disappeared and a significant number of them had been killed by predators, presumably because they were awake and vulnerable to attack when they would have been asleep.
-showing that it is a hugely important endogenous pacemaker.
Martin Ralph et al (1990)
-bred mutant hamsters with a 20-hour sleep/wake cycle.
-when scn cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters their cycles defaulted to 20 hours.
-both the animal studies emphasise the role of the scn in establishing and maintaining the circadian rhythm of the sleep/wake cycle.
Campbell and Murphy (1998)
-showed how light can be detected by skin receptor sites even when not by the eyes
-15 participants were woken at various times and a light pad shown on the back of their knees
-this produced a deviation from the sleep/wake cycle for up to 3 hours.
-suggesting that light is a powerful zeitgeber that doesn’t necessarily rely on the eyes to exert an influence on the brain.
social cues as an exogenous zeitgeber?
research suggests that a way of entraining circadian rhythms and beating jet lag is to eat and sleep at the local times as opposed to waiting for hunger and fatigue.
