The Biological Clock

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The Biological/body Clock (your endogenous pacemaker) – how does it work?

An endogenous (internal) mechanism

l  Thought to be generated by protein synthesis within the Supra Chiasmatic Nuclei (SCN). It’s in the hypothalamus.

l  How? …

l  Protein is produced for a number of hours until it reaches a level that inhibits further production. 

l  Then the level gradually falls, when it reaches a  ‘threshold’ level then production of the protein re-starts. 

l  This generates an internal (endogenous) biological rhythm – in humans of between 24 ½ and 25 hours.  

l  This endogenous rhythm is regulated to keep it in line with our environmental rhythms by an exogenous mechanism:

l  SCN have a nerve input directly from the retina of the eye, so they are kept informed about the zeitgebers of light and darkness.

l  In darkness this information is transmitted to the pineal gland which manufactures melatonin a hormone which stimulates the production of serotonin in the raphe nucleus. This hormone  causes reduced levels of arousal and so induces sleep.

l 

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