Circadian Rhythms Flashcards
Biological rhythms?
Biological event or function that is repeated through time in the same order with the sam interval.
Period?
Time that elapses before rhythms start to repeat itself.
Short - heart beat.
Monthly - menstural cycle
Annual - breeding, hibernation
Circadian rhythm?
Circa - around diem - day
Self sustained biological rhythm, period ~24hrs.
Biological clock?
Internal time keeping mechanism capable to driving/coordination a circadian rhythm - suprachiasmatic nucleus.
Zeitgeber?
‘Time giver’ - environmental time cue that entrains/resets biological rhythms.
Light is the pimary zeitgeber.
Actogram?
Horizontal axis - double plot of time.
2 sets of 24 hours - see how rhythm drifts.
LD, 12:12
DD
Are all rhythms endogenous?
No, some are directly driven by exogenous/external environmental rhythms. Eg barnacles.
Why do we have circadian rhythms?
Conserved through evolution.
Adaptation to life on a rotating world with regular light and dark periods.
Survival advantage - anticipate regular changes in environment.
Coordinate temporal organisation of function in individuals (correct sequence; food intake, increase GI tract sugar, increase aa transporters, increase enzymes to process.
Coordinate temporal organisation between individuals - eg mating.
List some biological, physiological, behavioural and pathological rhythms.
Biological - glucose uptake, metabolic rate, alcohol degradation, gene expression.
Physiological - core temp, BP, HR, platelet aggregation, hormones.
Behavioural - sleep/wake, drinking, food, pain threshold, motor skills, cognitive performance.
Pathological - MI, angina, ischemic stroke.
What is the chemical hand of the clock and where does it come from?
Melatonin.
Synthesised and secreted at night by the pineal gland.
Neural signals from the clock turns of transcription of mRNA for enzyme N-acetyltransferase which increases melatonin synthesis.
Reaches all cells - lipophillic etc,
Suprachiasmatic nuclei?
Small pairs nuclei, approx 10,000 neurones at base of optic chiasm.
Output - multi synaptic to the pineal gland. (And HR and BP)
Input - retinohypothalamic tract. Light receptor - subset of pRGC that detect light - photo pigment is MELANOPSIN.
6 properties of the biological clock?
1) free running under constant conditions
2) there is a clock in every cell (communication between SCN neurones is not required)
3) circadian clocks are affected by light. Light - glut from RHT - SCN and increase Ca, increase PK, phosphorylates CREB = regulate Per genes.
4) Temperature compensated
5) adjustable by zeitgebers.
6) under genetic control.
How are SCN neurones synchronised.
NO, VIP - diffuse messengers.
Melatonin feedback on SCN.
Explain the function of clock genes.
Make mRNA to protein transcription factor that work as pairs in the nucleus to regulate transcription itself. Auto regulatory feedback.
Many peripheral cells possess clock genes.
How does the SCN communicate with peripheral cells?
Hormonal - melatonin and glucocorticoids.
Metabolic - rhythm in food intake.
Behavioural - forced motor activity.
