Endogenous Pacemakers Flashcards
The suprachiasmatic nucleus SCN
The SCN is a cluster of nerve cells in the hypothalamus. It receives info about light because it’s located above the optic chiasma. Even when the eyes are shut, info about light is received by the SCN
The SCN is divided into a ventral and dorsal SCN in each hemisphere. Ventral SCN is easily reset by external cues and the dorsal SCN is less affected by external cues and more resistant to being reset.
The pineal gland receives signals from SCN about light which regulates production of melatonin which induces sleep by inhibiting the brain mechanisms that promote wakefulness.
AO2
The effect of the SCN has been demonstrated in animal studies. Morgan bred mutant hamsters with 20 hour circadian rhythms instead of 24 hours. He then transplanted the SCN of the bred hamsters into normal hamsters who showed the 20 hour rhythm. This demonstrates the key role the SCN plays as an internal biological clock. Study was based on animals and the anatomy of a hamster is very different to that of humans so findings may lack external validity. Ethical concerns.
Michel siffre demonstrated the existence of an endogenous pacemaker in his isolation study where he spent 6 months in a cave. His body settled into a sleep wake cycle of 25-30 hours showing that endogenous pacemakers exert an influence on circadian rhythms. CASE STUDY. Lacks Eco validity as he was in a cave which isn’t representative of real world settings.
There is also evidence to suggest there are other pacemakers and oscillators throughout the body and the SCN is not the only main one. Folkard et al studied a young women named Kate aldcroft who spent 25 days in a cave. After this period, her body temp rhythm was 24 hours while her sleep rhythm was on a 30 hour cycle. This demonstrates that there are separate endogenous pacemakers which can become desynchronised. CASE STUDY. Hormonal differences.
IDA
Such research is reductionist as it appears to see the SCN as the main endogenous pacemaker when research suggests there are various biological clocks throughout the body responsible for different rhythms. So this oversimplifies the way the human body works as in truth it is far more complex and we still don’t fully understand all of the rhythms and clocks.
The biological approach to explaining our rhythms is also deterministic as it ignores the role of free will we have in overriding these internal clocks. We can override them if we choose too.
