Discuss the Role of Endogenous Pacemakes in Biological Rhythms

A biological rhythm can is as any change in a biological activity that repeats periodically. They include rhythms with a frequency or periodicity of less than one day (ultradian), those with a periodicity of approximately one day (circadian), and those with a periodicity of greater than one day (infradian). These biological rhythms

are most often synchronized with daily, monthly, or annual cyclical changes in the environment. These external factors affecting biological rhythms are known as exogenous zeitgebers.A zeitgeber is an environmental cue, an environmental cue ,such such as the length of as the length of daylight or the degree of temperature that helps to regulate the cycles of an daylight or the degree of temperature that helps to regulate the cycles of any living organism's biological clock (or endogenous pacemaker). (or endogenous pacemaker)

The sleep-wake cycle is the most obvious of our biological cycles and is known as a circadian rhythm. A circadian rhythm is a cycle of about 24 hours and can be synchronized depending on which zeitgebers are present, this is mostly light and dark.

The biological clock in humans seems to be a small area in the hypothalamus- the suprachiasmatic nucleus (SNC)- whose neurons have an in-built circadian rhythmic pattern. The SCN regulates the production of melatonin in the pineal gland via an interconnecting pathway. Melatonin is a hormone which induces sleep. Another pathway connects the retina of each eye to the SCN. The amount of light falling on the retina influences the activity of SCN neurons and , indirectly, the release of melatonin from the pineal fland. So the link between light and melatonin production is maintained.

Morgan- mutant hamsters study→ support the SCN is an endogenous pacemaker and generates the rhythm in animals. (but lab conditions and ethical issues as causing harm)

The study of free-running biological rhythms involved a French cave explorer called Michel Siffre spent 6 months in an underground cave. The sleep pattern settled down to fairly regular pattern of between 25-30 hours that is slightly longer than 24 hours. The case of Michael Siffre may be dismissed as the study of just one unusual individual. However, we should consider the important role they play in helping us to understand the nature of circadian rhythms. Such studies offer an extremely rare insight into what happens when our body is left to "free-run" and therefore play a role in confirming what experimental studies involving larger groups have already suggested. Also suggests there are significant individual differences in these mechanisms. The cave man study shows how the body's sleep wake circadian rhythm is disrupted in the absence of external cues and, in effect, the role of exogenous zeitgebers in circadian rhythms. The sensitivity to light of the pineal gland and the SCN, the role of melatonin in controlling sleep and