Rhythms & Sleep Flashcards
(52 cards)
Circadian rhythms
Functions of a living organism that display a rhythm of about 24 hours
Diurnal animals
Like us
Nocturnal
Awake at night
Zeitgeber
A cue animals use to entrain or synchronize their schedules
Here, light is a zeitgeber to help entrain its cycle
Without any light cues
Without any light cues, the animal is still exhibiting a rhythm; it’s said to be free-running
Bottom portion is constant dim light
No zeitgeber, but still exhibits a rhythm
Circadian rhythms are generated by
An endogenous clock
Entrainment
The process of synchronizing the rhythm with external cues
Phase shift
The shift in activity in response to a synchronizing stimulus such as light or food
Period
Time between two similar points of successive cycles, may not be exactly 24 hours
A free-running animal
Maintains its own cycle without
external cues
Why have a circadian rhythm?
It synchronizes an animal’s behavior and body states to daily rhythms in the environment
The endogenous clock enables animals to anticipate an event and help with survival
Ex: nocturnal animal gets up too early, knows it needs to adjust and will do that accordingly
The hypothalamus houses a circadian clock
In the SCN– suprachiasmatic nucleus
Suprachiasmatic nucleus
Receives light input; responsible for programming time-keeping mechanisms
Lesions to SCN
Messes up rhythms
An animal uses light a little bit to help it synchronize
But without light, animal’s activity is all over the place
Circadian rhythms entrain to light-dark cycles using…
Different pathways, some outside of the eye
In amphibians and birds, the ___________ is sensitive to light
pineal gland
In mammals, light information goes from the eye to the SCN via the ________________
retinohypothalamic pathway
Retinohypothalamic pathway
Not all animals use it, but mammals do
Genetic component
Gene mutations show how important the clock is to behavior in constant conditions
Tau gene mutations
The period is shorter than normal
Double Clock gene mutants
Severely arrhythmic
Larks vs. night owls
People who feel energetic in the morning (“larks”) likely have different alleles of the Clock and per genes than “night owls”
Infradian rhythms
Some biological rhythms (infradian rhythms) are longer than a day, such as the 28-day human menstrual cycle
