Lesson 12 – Endogenous Pacemakers and Exogenous Zeitgebers Flashcards
Why do we have Endogenous Pacemakers and Exogenous Zeitgebers?
Our internal biological rhythms (circadian, ultradian and infradian rhythms) must be finely tuned in order to stay in keeping with outside 🌎
… we have endogenous pacemakers (internal biological rhythms) and exogenous zeitgebers (external cues/factors e.g. 💡) which reset our biological rhythms every day
What does Endogenous Pacemakers literally mean?
Within you time keepers
What is the most important endogenous pacemaker?
Suprachiasmatic nuclei (SCN)- tiny cluster of nerve cells in hypothalamus
What is the role of the Suprachiasmatic nuclei?
SCN plays important role in generating circadian rhythms- acts as master ⏰ linking other 🧠 regions that control 💤 and arousal
ALSO controls all other biological ⏰s throughout body
How does the SCN work as an endogenous pacemaker?
Neurons within SCN synchronise with each other so that their target neurons in sites elsewhere in body receive time-coordinated signals
These peripheral ⏰ can maintain a circadian rhythm BUT ✖️ for long which is why controlled by SCN
Possible because of SCN’s built in circadian rhythm- only needs resetting when external 💡 levels change- SCN receives info about 💡 levels through optic nerve- if biological ⏰ running slow then morning 💡 shifts ⏰
What else is the SCN responsible for?
SCN also regulates manufacture and secretion of melatonin in pineal gland via interconnecting neural pathway
SCN sends signal to pineal gland directing it to ⬆️ production and secretion of hormone melatonin (induces sleep by inhibiting 🧠 mechanisms that promote wakefulness) at 🌓 and to ⬇️ it as 💡 levels ⬆️ in morning
What are the evaluation points for Endogenous Pacemakers?
👍- Folkard (1996)- studied university student, Kate Aldcroft, who spent 25 days in lab 🧪 - had ✖️ access to 🌞light or other exogenous zeitgebers that might have reset SCN- at end of 25 days her core 🤒 rhythm still at 24 hours
👎- BUT, Kate Aldcroft’s 💤-wake cycle extended to 30 hours, with periods of 💤 as long as 16 hours … we do need external influences to maintain our circadian rhythms
What is an exogenous zeitgeber?
Exogenous (refers to anything whose origins are outside of the organism) zeitgebers- environmental events responsible for maintaining biological ⏰ of organism
What is the most important Exogenous Zeitgeber for most animals?
Light 💡
What is the role of light as an exogenous zeitgeber?
- Receptors in SCN sensitive to changes in 💡 levels during day ☀️use this info to synchronise activity of body’s organs and glands
- 💡 resets internal biological ⏰ each day- keeping it on a 24-hour 🚲
- Melanopsin (protein in retina of 👁)- sensitive to natural 💡- critical in this system
What about those who move to a different time zone or work night shifts?
- When ppl move to 🌓 shift or go to country with different ⏰ zone their endogenous pacemakers impose their inbuilt rhythm of 💤 (circadian rhythm) BUT this now out of synchrony with exogenous zeitgeber (💡)
- Disrupted biological rhythms-> disrupted 💤 patterns, ⬆️ anxiety and ⬇️ alertness and vigilance
What are the evaluation points for Exogenous Zeitgebers?
👍- Skene and Arendt (2007)- found that vast majority of blind subjects who still have some 💡 perception have normal circadian rhythms- ppl without 💡 perception show abnormal circadian rhythms
👍- Burgess et al. (2003)- found that exposure to bright 💡 prior to an east-west ✈️ ⬇️ the ⏰ needed to readjust to local ⏰ on arrival
👍- Vetter et al. (2011)- compared 💤-wake and activity-rest patterns of 2 groups of pps over 5 week period
- 1 group remained in normal warm artificial 💡- BUT other group experienced artificial blue 💡- all pps kept daily 💤 log and wore devices that measured their movement- pps under warm 💡 synchronised their circadian rhythms each day with natural 💡 of dawn BUT pps exposed to blue 💡 synchronised their patterns to office hours (💻 screen etc)
