Circadian rhythms Flashcards
What is an endogenous pacemaker?
An internal biological clock mechanism that maintains regular bodily rhythms.
What are exogenous zeitgebers?
External ‘time-givers’ (for example, light) that give clues to the time of day/year.
What is the Suprachiasmatic nucleus (SCN)?
Located in the hypothalamus in the brain, the SCN is the body’s main endogenous pacemaker.
Can receive info about light levels to keep our bodily rhythms in synchrony with the environment.
What are infradian rhythms and some examples?
Bodily cycles that occur less frequently than once a day.
E.g. the menstrual cycle (approx every 28 days.)
others: seasonal affective disorder (SAD), a seasonal form of depression.
In non-human animals: hibernation, migration and reproduction can occur on seasonal cycles too.
Example of a study on Infradian rhythms
Stern and McClinktock took samples of pheromones from a group of women (donor group) and applied this to another group of women (recipient group).
Found menstrual cycles of recipient women influenced by cycles of donors.
Suggests pheromones act as an exogenous zeitgeber that can influence the menstrual cycle.
What are ultradian rhythms and give some examples?
Bodiy cycles that occur more than once a day.
E.g. the stages of sleep (approx every 90 minutes).
others: basic rest and activity cycle (BRAC) -> humans tend to demonstrate 90 minute cycles of activity and rest.
Example of a study on ultradian rhythms
Dement and Kleitmen (1957) used an EEG in a sleep lab to show that rapid eye movement (REM) sleep occurred every 92 minutes on avg.
Supports the notion of an endogenously controlled ultradian rhythm.
What are circadian rhythms and give some examples
Bodily cycles that occur once a day.
E.g. The sleep-wake cycle.
Others: melatonin (a sleep hormone) peaks at midnight while cortisol (a stress-related hormone) is at its lowest at midnight.
what are photosensitive cells?
They contribute to regulation of pupil size and other behavioural responses to ambient lighting conditions.
What are biological clocks?
Organisms’ natural timing devices regulating cycle of circadian rhythms composed of specific molecules (proteins) that interact with cells throughout the body.
Nearly every tissue and organ contains biological clocks.
What is a master clock?
Coordinates all biological clocks in a living thing, keeps clocks in sync.
In vertebrate animals this is a group of about 20,000 neurons that form a structure called the suprachiasmatic nucleus, or SCN.
