endogenous pacemakers and exogenous zeitgebers Flashcards
what are endogenous pacemakers and exogenous zietgebers ?
Our internal biological rythmns need to be reset constantly so they stay in synch with the outside world. to do this our body has exogenous zietgebers (external cues /factors) and endogenous pacemakers ( internal biologial rythmns). These reset our biological rythmns everyday
endogenous pacemakers
The most important endogenous pacemakers is the suprachaismatic nuclei (SCN) , these are a tiny cluster of neurons located in the hypothalamus.
SCN play an important role in creating our circadian rythmns , neurons within the SCN sync with eachother leading to their target neurons in other areas of the body receive the correct time cordinated signals. These peripheral clocks can maintain a circadain rythmn for a bit but for long so they need to controlled by the SCN with a built in circadian rythmn.
It also controlls sleep by sending signals to the pineal gland telling to produce and secrete more melatonin night and decrease at day due to changing light levels. Melatonin promotes sleep in high levels.
endogenous pacemakers evaluation
+) Folkard studied a university student called Kate who spent 25 days in a lab without the exogenous zietgebers of light which could reset the SCN. Despite this after 25 days her core tempreture rythmn was still 24 hours indicating exogenous zietgebers are not needed to maintain our internal biologil rythmns.
-) However Kate’s sleep-wake cycle was extended to 30 hours with periods of sleep as long as 16 hours, this suggests that we do need exogenous zietgebers to maintain internal biological rythmns
exogenous zietgebers
exogenous zietgebers are enviromental events that maintain the biological clock of an organism , for most animalsthe most important one is light.
Receptor SCN are sensitive to changes in light during the day and use this information to synchronise the activities of the bodies organs and glands. The light keeps the body on a 24 hour cycle , Melanopisn is a protein in your eye retina which is critical for this process.
Peoples bodies can have out of synch exogenous zietgebers when compared to the endogenous pacemakers if they travel to a different time zone as the light levels will be different but your endogenous pacemakers will still want you to sleep at certain times.
Out of sync biological rythmns lead to disrupted sleep patterns , inreased anxiety and decreased alterness and vigilance.
exogenous zietgebers evaluation
+) The vast majority of blind people who still have light perception still have circadian rythmns while blind people without light perception have abnormal circadain rythmns. This shows how exogenous zietgebers maintain our internal rythmns.
+)Burgess et al found that ezposure to bright light before east-west travel reduces the amount of time for your circadain rythmn to adjust.
-) In the Artic the sun does not set during the summer months and studies of individuals who live there show they have normal sleeping pattern despite prolonged light exposure. this suggests that exogenous zietgebers have little affect on our internal biological rythmns.
