Biological Rhythms Flashcards
Morgan
Removed the SCN from hamsters and found this resulted in a disappearance of their circadian rhythm. The circadian rhythm could be re established by transplanting SCN cells from foetal hamsters, supporting the central role of the SCN as a pacemaker.
Morgan and Ralph
Transplanted SCN cells from mutant hamsters ( those who were bred to have shorter cycles than 20 hours) and found that transplanted hamsters took the mutant rhythm. When transplanting SCN normal 24 hour cycle to mutants, the mutant hamsters took the 24 hour cycle within 6/7 days and the recipients rhythm no longer matched their own genes but the genes of SCN donors. Supports the central role of SCN as an endogenous pacemaker.
Siffre
Spent 6 months in a cave with no natural sound or light. Initially he experienced a erratic sleep wake cycle, however settled into a regular pattern of a 25 hour circadian rhythm rather than a 24 one. Concluded that endogenous factors can influence sleep wake cycles in the absence of light. Main zeitgeber in the study was light, presence of light is necessary for the biological rhythm to be coordinated with the outside world - exogenous factors can also influence biological rhythms
Aschoff and Weaver
Human endogenous pacemakers tend to run slightly slower than 24 hours and needs to be synchronised each day through exogenous zeitgebers
Luce and Segal
People who live in arctic would sleep for 6 months if their cycle was only controlled by endogenous factors. However, they found that they slept for 7 hours a night and social customs have become their dominant zeitgeber.
De Coursey
30 chipmunks had their SCN removed and then returned to their natural habitat. After 80 days, found that significantly more chipmunks had been killed compared to the control group with intact SCN. Suggesting that the chipmunks were killed as they stayed awake, therefore to rely solely on exogenous factors could threaten survival.
