Biological Clocks Flashcards
what is biological clock theory
Animals have a timing mechanism with an endogenous, built in schedule, independent of environment
What is environment response theory
Relationships between command centers are modified by feedback from the environment… behavior changes as conditions change
What is the environment response theory for crickets
If cricket calling is controlled by environment, crickets in constant light should never call
What was the first cricket calling experiment
Grow crickets in lab under constant temperature/brightness, record calling
What were the results of the first cricket chirp experiment
Crickets continue calling in absence of environmental cue
What was the interpretation of the cricket chirp experiment
Mate calling is a free-running cycle, supporting idea that internal clock controls behavior
What is the time period of a circadian rhythm
“about a day”
What was the second cricket calling experiment
Grow crickets in lab on 12 hour light dark cycle and record calling
What were the results of the second cricket calling experiment
Crickets use the cue of darkness to adjust their calling so that it begins about 2 hours before lights off and ends about 2.5 hours before lights on
What was the interpretation of the second cricket calling experiment
Calling is reset/entrained each day to darkness, which matches the natural behavior
What hypothesis was supported by the cricket experiments and why
Both hypotheses: calling can occur independent of environment based on an internal clock but is normally reset each day during nightfall
What is the circadian rhythm pathway?
Sunlight/environmental cue -> sensory receptors -> pacemaker -> observed rhythms
What are sensory receptors considered
Clock-setting pathway
What is the pacemaker considered
Clock mechanism
What are the 4 observed rhythms in circadian rhythms
Locomotory patterns
Feeding behaviors
Hormone release patterns
Other rhythms
What structure is the “mammalian pacemaker”
Superchiasmatic nucleus (SCN)
What is the input to the SCN
Retina
What happens when SCN is removed from rodents
Arrhythmic patterns of locomotion, hormone secretion, feeding
What happens during transplant of SCN but noth other tissues
Locomotion, hormone secretion, feeding restored
what happens during transplant of mutant SCN
Mutant period length (shorter/longer than 24 hours)
What does the SCN do when removed from the brain
Maintains rhythmic secretions
*Research clock/per gene and add it to this
:(
What is the evidence for per as a timing gene (4)
Fruitfly mutations
Normal honeybee levels vary with behavior
Humans with a per mutation have altered sleep cycles
Gene is highly conserved and expressed in SCN
Explain honeybee per variation
Young nurse bees have low per and are active all day/night
Adult foragers, who go out during day, have higher per levels and exhibit defined circadian rhythms
What are the three expectations of the biological clock
Molecule relaying clocks instructions should be regulated by clocks genes
Molecule should be secreted and there should be a receptor for secretions in target behavior mediating tissue
Experimental manipulation of chemical should disrupt timing of behavior
What are the 2 candidate molecules for the “biological clock”
Melatonin and PK2