Endogenous pacemakers and exogenous zeitgebers Flashcards
What is an exogenous Zeitgebers (EZs)
Stuff happens outside - external cues that may affect or entrain our biological rhythms
Examples of exogenous Zeitgebers EZs
Social cues and light
What is an endogenous pacemakers Eps?
Internal mechanisms - that regulate our biological rhythms
EP body example
Internal biological clock (SCN)
What is the Suprachiasmatic nucleus (SCN)
Acts as a master clock linking the brain regions that control sleep and arousal
Where is the SCN located?
A tiny bunch of nerve cells located in the hypothalamus in each hemisphere of the brain
* One of the primary endogenous pacemakers and is influential in maintaining circadian rhythms such as sleep and wake cycle
What resets the circadium rhythms?
However the rhythm is reset by external cues (EZs) so it can respond to environmental changes
Where does SCN receive info from?
Light info from the optic nerve
What is the pineal gland?
responds to signals from the SCN and releases melatonin (sleep hormone) to increase secretion and night and decrease levels as light increases in the mornings
The pineal gland and the SCN jointly function as endogenous pacemakers in the brain their sensitivity to light and role of melatonin mean their activity must be synchronised with light/ dark rhythm outside
How does light affect the circadian rhythms?
Light resets the internal bodily clock keeping on a 24hr cycle
What are the social cues as EZs?
Social cues - such as mealtimes and social activities may act as a EZ
How do EZs and EPs interact?
- Light enters eye and is processed
- The optic nerve transfers the information about light to the SCN
- The SCN regulates the pineal gland to relase melatonin
- Causes the sleep wake cycle
What does melatonin do?
a sleep hormone that produces sleep
Morning - interaction of EZs and EPs
Morning → Optic nerve receives light transfers information to SCN → stimulates pineal gland to decrease Melatonin ( sleep hormone)
Night EZs and EPs interaction
Optic nerve receives decreased light transfers information to SCN → stimulates pineal gland to increase Melatonin ( sleep hormone)
Strengths of EZs and EPS
- Mutant hamsters study
Genetic breeding of hamsters with a 20 hr rhythm
SCNs removed and transplanted into normal hamsters - had an impact of gaining a 24hr sleep cycle
This increases support for existence SCN as the main endogenous pacemaker in the sleep-wake cycle - Evidence light is EZ
27 office workers in an experimental group exposed to strong blue light, they shift their cr to match office lighting
Control group - 27 office workers with normal office lighting rhythms matched shifting time of natural light of dawn
Strongly suggests light is an EZ and artificial light can disrupt EPs overriding natural light as primary EZ - Real world application
Light exposure to avoid jetlag
Exposure to bright light prior to E-W flight decreased the time needed to readjust to local time on arrival
This can shift the rhythm up to 2hrs with continuous bright light
Realworld utility and application of this theory
EZs and EPs interactions strengths
Aldcrodt spent 25 days in a lab with no EZs → had to play ‘amazing grace’ on bagpipes at the same time every days → found sleep-wake cycle slipped into the 30-hr period
what happens when you have disruption to the rhythms?
- ^ anxiety
- less alert
- less vigilent
