Outline and evaluate research into endogenous pacemakers and exogenous zeitgebers in two biological rhythms. (9 + 16 marks)
Ans). Circadian rhythms occur over a 24 hour cycle. In the early 1970's, researchers discovered that the endogenous pacemaker responsible for this rhythm was located in a part of the hypothalamus called the suprachiasmatic nucleus (SCN). Stephan and Zucker (1973) found that damaging the SCN in rats affected a number of circadian rhythms, including drinking and wheel-running. In other research, Inouye and Kawamura (1979) kept SCN tissue alive in an organic culture and found that the cells continued to show circadian rhythms.
Further support for an endogenous pacemaker in the SCN comes from Ralph et al (1990). They transplanted the SCN of a hamster with a mutated 20.2 hour rhythm into the brain of a hamster with a normal 24 hour rhythm. On recovery, the hamster began showing behaviours following the shorter circadian rhythm of the donor. This research might be accused, however, of being a little too reductionist. It is focusing very much on the cellular activity of a very small part of the brain, and does not seem to be considering the importance of environmental influences on rhythms.
There is research suggesting that environmental factors are important in maintaining a circadian rhythm. Without light as a zeitgeber, after 205 days…