AO1

• The suprachiasmatic nucleus is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere
• scn is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms
• nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the left and right visual area of the cerebral cortex
• the SCN lies just above the optic chiasm
• SCN receives information about light from the optic chiasm, this continues even when our eyes are closed enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep
• Decoursey et al destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
• The sleep/wake cycle of the chipmunks disappeared and by the end of the study alot of the chipmunks had been killed by predators
• Ralph et al bred mutant hampsters with a 20 hour sleep/wake cycle
• When SCN cells from the foetal tissue of mutant hampsters were transplanted into the brains of normal hampsters the cycle of the second group defaulted to 20 hours
• The SCN passes the information on day length and light that it receives to the pineal gland
• The pineal gland is another endogenous mechanism guiding the sleep/wake cycle
• during the night the pineal gland increases production of melatonin, a chemical that induces sleep and is inhibited during periods of wakefulnees