Endogenous Pacemakers, Exogenous Zeitgebers Essay

Topics: Circadian rhythm, Melatonin, Pineal gland Pages: 2 (683 words) Published: April 25, 2011
Endogenous Pacemakers, Exogenous Zeitgebers Essay Plan

1.Describe in detail endogenous pacemakers- suprachiasmatic nucleus (SCN) in the hypothalamus, SCN obtains information about light from the eye via the optic nerve, happens even when eyes are shut, as light penetrates the eyelids. If endogenous clock is running slowly, morning light automatically shifts the clock ahead, making the rhythm correct with the world outside again. SCN- pair of structures- one in each hemisphere of the brain, and each of these is divided into a ventral and dorsal SCN. Albus found that the ventral SCN is relatively quickly reset by external cues, but the dorsal SCN is much less affected by light and more resistant to being reset. SCN sends signals to the pineal gland making it produce melatonin at night, melatonin creates sleep because it inhibits the brain mechanisms that promote wakefulness.

2.Describe in detail exogenous zeitgebers- resetting the biological clock (entrainment). Light resets the SCN, also resets other oscillators located throughout the body as the protein CRY, part of the protein clock is light sensitive. Darlington- morning two proteins bind together CLOCK and CYCLE, once joined, CLK-CYC produce two more proteins, PERIOD and TIME (PER-TIM). PER-TIM makes CLK-CYC inactive, as PER-TIM increases CLK-CYC decreases and PER-TIM decreases as well (takes about 24 hours).

3.Critical Point 1: This explanation for the role of the Suprachiasmatic Nucleus is reliable. Morgan bred “mutant” hamsters so they had circadian rhythms of 20 hours instead of 24 hours and then transplanted their SCN’s into normal hamsters. He found that the normal hamster displayed the mutant rhythms. Therefore, this implies there is strong evidence to support the theory.

4.Critical Point 2: However, there is a methodological flaw to the majority of the studies carried out on this topic. This is they have been performed on non-human animals. As a result of this, it is difficult to...
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