Endogenous Pacemakers, Exogenous Zeitgebers

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ENDOGENOUS PACEMAKERS

-The main endogenous pacemaker is a cluster of nerves called the suprachiasmatic nucleus which is located in the hypothalamus. It obtains info about light from the eye via the optic nerve, even when they are closed. Morning light van automatically shift the clock ahead if the endogenous clock is running slow. 

-Divided into ventral and dorsal SCN ... ventral is relatively quickly reset by external cues whereas dorsal SCN is less affected by light.

-SCN sends signals to pineal gland to increase melatonin at night, which induces sleep.

EXOGENOUS ZEITGEBERS

-Entrainment is resetting the biological clock with exogenous zeitgebers.

-Light is the dominant zeitgeber as it can reset the body's main pacemaker, the SCN. 

-Cryptochrome is light sensitive.

-Until recently, biologists thought social cues were the main zeitgebers for human circadian rhythm, as out daily rhythms appear to be entrained by social convention. Light is the dominant zeitgeber.

-The variations in…

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