Role of Endogenous Pacemakers

Both endogenous pacemakers and exogenous zeitgebers help maintain and control the sleep wake cycle. Endogenous Pacemakers are internal “biological clocks” that manage our rhythms, although they are our internal time keepers and work most effectively with the aid of exogenous zeitgebers (external cues such as light and dark), the endogenous pacemakers can run without the input of external cues, however it is likely that the day will lengthen to roughly 25 hours.  
The endogenous pacemaker in mammals is found in the suprachiasmtic nucleus (SCN), a cluster of nerve cells located in the hypothalamus. Here the sunlight is detected and our sleep wake cycle is adjusted to be in time with the environment. The result of this is the SCN stimulating the pineal gland to produce more melatonin that induces sleep by inhibiting the mechanisms that crate wakefulness.
Circadian rhythms are biological rhythms that occur within 24 hours. The most common circadian rhythm is the sleep-wake cycle. It is normally governed by EZs such as light, but is inherently an endogenous body clock. Aschoff and Wever showed that without any EZs participants followed a circadian rhythm. This proves that even without the affect of external cues, the sleep-wake cycle is an internal body clock. Siffre showed the flexibility of the circadian rhythm and the vast importance of EP by living for six months in a cave with very few EZs that changed the rhythm from the standard 25 hour to 48 hours. Siffre then hypothesised that the main EZ in the sleep-wake cycle was light and it’s affect on melatonin, and more importantly EZs in general are the most important variable in manipulating biorhythms, contradicting the previous research on SCN activity. However, it is an idiographic study that lacks ecological validity, and not all external cues were removed, for example the role of artificial light could have easily manipulated the biorhythm and misplaced for the role of other variables. We are therefore unable...