Endogenous pacemakers and exogenous zeitgebers

AO1

EP The suprachiasmatic nucleaus: SCN is group of nerve cells in the hypothalamus in both hems. It maintains the sleep/wake cycle. Nerve fibres connect to each eye across the optic chiasm on their way to the visual area in the cerebral cortex. The SCN lies above the optic chiasm and recieves info about light from this structure. This allows the biological clock to adjus to changing sunglight patterns even when we're asleep.

Animal studies and the SCN: DeCoursey destroyed the SCNs of 30 chipmunks, returned them to their habitat and observed them for 80 days. The sleep/wake cycle disappeared and many were killed possibly because they were awake and vulnerable to attack. 

EP Pineal gland and melotonin: The SCN passes info about light to the pineal gland which is behind the hippothalamus. In the night, the pineal gland increases the production of melotonin which induces sleep and is inhibited during periods of wakefulness.

EZ Light: Resets the main endogenous pacemaker - the SCN. Light also affects hormone secretion and blood circuation. Campbell and Murphy show that light can be detected by skin recpetor sites when it is not recieved by the eyes. 15 participants were woken at different times and a light pad was shone on the back of their knees which produced a deviation in their usual sleep/wake cycle of up to 3…