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.