PAPER 2 - Biopsychology - Endogenous pacemakers and exogenous zeitgebers Flashcards
(7 cards)
Define endogenous pacemakers.
Internal body, clocks that regulate many of our biological rhythms, such as the influence of suprachiasmatic nucleus (SCN) on the sleep/wake cycle.
Define the 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, such as the alternation of night and day.
What is suprachiasmatic nucleus (SCN)?
The suprachiasmatic 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 the mammalian species
- influential in maintaining circadian rhythms such sleep/wake cycle
- nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area of the cerebral cortex
- lies just above the optic chiasm and recieves info about light directly from this structure
- continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep
Discuss animal studies and the SCN.
DeCoursey et al. 2000 = destroyed SCN connections in the brains of 30 chipmunks, returned to their natural habitat, observed for 80 days.
Sleep/wake cycle disappeared and a significant proportion of them had been killed by predators.
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 or normal hamsters, the cycles of the second group defaulted to 20 hours.
Both studies emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
SCN and the pineal gland and melatonin.
The SCN passes info on day length and light that is receives to the pineal gland.
Night: pineal gland produces melatonin - induces sleep. Causal factor in seasonal affective disorder.
Define exogenous zeitgebers.
External cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle.
Discuss light as an exogenous zeitgeber.
Light can reset the body’s main endogenous pacemaker, the SCN, and plays a role in the maintenance of the sleep/wake cycle. Aso has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation.
