Endogenous pacemakers and exogenous zeitgebers

definitions-  Endogenous pacemakers; internal ody clocks that regulate many of our biological rhythms, such as the influence of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle, Exogenous zeitgebers; external cues that may affect or entrain our biological rhythms such as sleep/wake cycle

Endogenous pacemakers

The suprachiasmatic nucleus (SCN)-

tiny bundle of nerve cells in hypothalamus and influencial in maintaining circadian rhythms, lies just above th optic chiasm and recieves info about light directly from that structure

Animal studies and the SCN-

DeCoursey et al: destroyed SCN connections in chipmunks and returned to habitat, sleep/wake cycle disappeared and many killed by predators presumably due to being vulnerable as awake.

Ralph et al: bred mutant hamsters with 20 hour sleep/wake cycles, transplanted SCN cells from foetal tissues of the mutants into brains of normal hamster who then developed 20 hour cycle

both emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle

The pineal gland and melatonin-

the SCN passes info on day lenght to pineal gland that controls melatonin production to induce sleep, also suggested to be a casual factor in SAD

Exogenous zeitgebers

Zeitgebers-

reset biological clocks and entrains cycles as without external cues, free-running biological clocks continue in a cyclical pattern

Light-

can reset the SCN and has indirect influence on key processes such as hormone secretion and blood circulation. Campbell…