endogenous pacemakers

Question 1

SCN (suprachiasmatic nucleus)

Answer 1

tiny bundle of nerve cells in BOTH HEMISPHERES of hypothalamus
-one of primary endogenous pacemakers in mammals
-nerve fibres connected to eye cross in optic chiasm
SCN lies above optic chiasm
- receives info about light, continues when eyes are closed to allow biological clock to adjust to changing patterns of daylight

Question 2

animal studies CHIPMUNK

Answer 2

1) DeCoursey destroyed SCN of 30 chipmunks then returned to their habitat and observed for 80 days
FOUND sleep/wake cycle was destroyed and by the end, significant amount had been killed by predators

Question 3

animal studies HAMSTER

Answer 3

2) Ralph bred ‘mutant’ hamsters with 20 hr sleep wake cycle
SCN cells from foetal tissue of mutant hamsters were transplanted into brains of normal hamsters and cycle of 2nd group defaulted to 20hr

Question 4

pineal gland / melatonin

Answer 4

SCN passes info on day length and light that it receives to pineal gland
- during night, pineal gland increases prod. of melatonin, a factor of SAD