Are rhythms that are not imposed by the enviroment
but generated from within the organisms
As many biological cycles follow a 24 hour rhythm, even in the absence
of external stimuli, there must be an internal biological pacemaker
The main pacemaker is the Super Charismatic nucleus (SCN) a small group of cells
in the hypothalamus generating a circadian rhythm reset by light entering the eyes
Role of SCN
Morgan (1995) bread hamsters to have 20 hour
circadian rhythms instead of 24 (mutants).
Transplanted SCN into normal hamsters. Which
now show 20 hour circadian rhythm
Chipmunks. DeCoursey et al. (2000) removal of
SCN in chipmunks led to more deaths. Circadian
rhythms disruptive likely that chipmunks more
active and detected by predator. Shows
importancee adaptive functioning of body clock.
issues of ethics and generalisability
Evidence for centeral and pheripheral oscillators
Kate Aldcroft. cave study for 25 days, temperature
still at 24 hour cycle, but sleep on 30 hour cycle