Circadian Biological Rhythms Flashcards
What is meant by a biological rhythm?
Change in body processes or behaviour in response to cyclical changes
What do biological rhythms involve?
Repetitions of certain physiological processes
When are they most often synchronised?
daily or monthly
What is determined by the length of time that a complete cycle takes until it begins again?
The type bodily rhythm it is classified as
Periodicity and example of a Circadian Rhythm?
Approx once a day i.e every 24 hours
sleepwake cycle
Periodicity and example of a Ultradian Rhythm?
More frequentely than once a day i.e shorter than 24 hours
Sleepcycle
Periodicity and example of a Infradian Rhythm?
Less frequentely than once a day i.e longer than 24 hours
Menstrual cycle
The circardian rhythm of the sleepwake cycle relies on both…?
Internal and external factors to control it.
What is meant by an Endogenous pacemaker?
Internal factors in the brain
What is meant by an Exogenic Zietgiber?
External factors in the environment.
What is the main endogenous pacemaker?
Suprachiasmatic Nucleus (SCN)
What and where is the SCN?
Small bundle of neurons located above the optic chiasm
Has an internal activity rhythm which persists even when isolated from the brain
How long will the SCN ‘free run’ in the absence of external cues?
Approx 25 hours instead of 24.
What is second endogenous pacemaker is known as and what is it responsible for?
Pineal gland, pes shaped gland
converting serotonin to melotonin
What happens when melotonin is released into circulation?
Acts on the brain’s sleep mechanisms
causing a reduction in alertness and drowsiness
Example of Exogenous Zeitgebers (external environmetal stimuli) that work with endogenous pacemakers?
Light and social cues i.e seasons, work etc.
The SCN is reset set every morning by what?
Light onset
The visual receptors in the retina part of the eye recieve the light signal and activate what?
Retinohypothalamic tract pathway
This pathway alerts the SCN and pineal gland affecting what?
melotonin production.
Daylight inhibits the release of what?
melatonin
and darkness induces sleep
When travelling across time zones, what happens to the (SNC) endogenous pacemakers and exogenic zeitgebers (destination time)?
They become unsynchronised
What times these rhythms dictate and what happens to them?
Eating, sleeping, hormone regulations and body temperature.
They no longer correspond to the environment.
Jet lag refers to?
The body not being able to immediately realign these rhythms.
What does the SCN need to do in this new environment?
Entrain (resynchronise) which may take several days
How does working at night disrupt Endogenous Pacemakers and Exogenous Zeitgebers working together?
SNC will be unsynchronised with available cues from exogenous zeitgebers such as daylight.
What type of shifts causes the biggest disruption in circadian rhythms?
Backward rotating shifts
What creates a risk of heart disease and cancer for shift workers?
hormone production (melotonin released during working hours)
lack of sleep (daytime sleep is more disrupted)
unhealthy eating (leads to irritability and decreases alertness)
What are endogenous pacemakers responsible for?
regularity
What are exogenous zeitgebers responsible for?
entrainment
Practical applications of increasing productivity in shift workers include?
Follow forward rotating shifts
reduze ex and ep disruption by using bright lights during night shifts to mimick daylight.
teenagers circadian rhythms are typically how much later than adults?
2 hours
Study by ox, 10am starts 19% exam improvment
How does research into the control of the sleepwake cycle impace the econmy?
It has positive implications
What does evidence from HUMAN studies do?
Support the role of INTERNAL endogenous pacemakers in the sleepwake cycle
What did french speleogist Michel Siffre not have access to for 179 days un a subterranean cave?
Living in isolation he had no access to any exogenous Zeitgebers eg sound, calenders, or daylight
Although erratic at first, his sleep cycle settled do to a regular..?
25-30 hour cycle.
What is the sleep wake cycle largely controlled by?
Endogenous Pacemakers
What is the sleep wake cycle entrained by?
exogenic zeitgebers
What does evidence from ANIMAL studies support?
The role of INTERNAL endogenous pacemakers in the sleepwake cycles
What was shown by mutant hamsters selectively bred to have a 20 hour sleepwake cycle? Ralph et al 1990
SNC cells from mutant hamsters transplanted to brains of hamsters with normal sleepwake cycle.
Normal Hamster’s Cycle began to alter and changed to the 20 hour of the donor mutant.
What do these findings do to the validity of the function that endogenous pacemakers have in the sleepwake circadian rhythm?
Increases the validity of the key role of regularity
Why is it difficult to make generalisations from supporting research?
One individual studied who was used to those conditions
can’t generalise = unrepresentative of everyone’s circadian rhythm
in animal research: extrapolation of findings = invalid explanation in human
exposed to different physicological structures, different ez’s affecting sleepwake cycles eg. clocks
Why is it difficult to draw conclusions about the role of endogenous pacemakers?
same sample sizes in human studies
use of animal research
