clocks. clocks: what is a clock? how does a biological clock compare with a mechanical clock? why...
Post on 20-Dec-2015
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Clocks:
What is a clock?How does a biological clock compare with a mechanical clock?Why have a circadian clock?What are the properties of circadian clocks?How do we set the circadian clock?
All clocks must have two basic components:
1. a regular, constant or repetitive process or action or OSCILLATION to mark off equal increments of time
2. a means of keeping track of the increments of time and displaying the result.
Mechanical Clock
Oscillator: a regular, constant or repetitive process or action to mark off equal increments of time.• Pendulum• Balance wheels• Vibrating crystal - quartz• electromagnetic waves – atomic clocks
Output: a means of keeping track of the increments of time and displaying the
result.• position of clock hands• digital time displays.
MECHANICAL CLOCKS
Pendulum clock 1656 Christiaan Huygens
1721 George Graham
1889 Siegmund Riefler
Balance Wheels 1876
Quartz clocks 1920’s
1969 Seiko
1972 Pulsar
1980 Swatch
Atomic clocks 1955 cesium
Mechanical Clock
Oscillator: a regular, constant or repetitive process or action to mark off equal increments of time.• Pendulum• Balance wheels• Vibrating crystal - quartz• electromagnetic waves – atomic clocks
Output: a means of keeping track of the increments of time and displaying
the result.• position of clock hands• digital time displays.
Resetting Mechanism•manual
Biological Clock
Oscillator: pacemaker neurons
Output: overt biological rhythms
Resetting Mechanism - zeitgeber
Anticipation
Properties of Biological Clocks
They continue to run under constant conditions.
tau = not exactly 24h
They are Temperature Compensated
They are affected by Light Intensity.
They are under Genetic Control.
They are Adjustable
Zeitgeber
Range of Entrainment
Why have a circadian clock?
Coordinates body activities with each other
Synchronizes individual’s activity with the environment
Anticipates predictable rhythmic changes in our environment
Gives animal best chance for survival
Suprachiasmatic Nucleus (SCN)
Neuropeptides
VIP (vasoactive intestinal polypeptide
GRP (Gastrin releasing peptide)
PHI (peptide histidine isoleucine)
Dorsomedial divisionVentrolateral Division
Criteria for identification of the clock:
Ablation eliminates circadian rhythms Electrolytic Lesion Chemical Lesion
Circadian rhythm of activity exists within the clock Electrophysiological Metabolic -2Deoxyglucose Neurochemical synthesis
Isolation of clock from rest of brain in vivo eliminates overt rhythms but does not eliminate rhythm within the clock.
Remove clock from the animal and clock still exhibits a sustained circadian rhythm
Transplant clock cells back into lesioned, arrhythmic animal restores rhythms
Rhythmic Activity in situ
Inouye and Kawamura – 1970s – Electrical Activity
Schwartz et al – 1980 – Metabolic Activity
Rhythms within SCN
Electrical activity – high during day, low at night
Metabolic activity – active during day; inactive at night
Neurotransmitter synthesis
Oscillator
Lesion
Arrhythmia
Ablation
Humoral
SCNx
temporal
A structure exhibiting a regular variation
Injury
Without a rhythm
Total removal
Transported in the blood
SCN lesioned
Related to time
Tau mutant A circadian period different from 24h
Wild type Non-mutant, control organism
Homozygous 2 identical alleles for a trait
Heterozygous 2 different alleles for a trait
In vitro in an artificial environment outside the
living organism
In vivo In the living organism
Electrode An instrument which conducts an
electric current
Explant tissue removed from its normal place of
growth and placed into tissue culture
Organotypic
Electrolyic made with an electricl current
Torpor dormant or lethargic state