L14 - Biological rhythms Flashcards
How do organisms on earth adapt to the cyclical changes?
- Passively/retroactively e.g Homeostatic mechanisms
- Proactively e.g Biological timekeepers
What are examples of things effected by circadian rhythms?
- Body temperature
- Hormone secretion (e.g. melatonin, cortisol)
- Locomotor activity
- Sleep
- Alertness/cognitive performance
- Muscle strength
- Immune function
What provides a simple way of
studying circadian rhythms in the wild and in the lab?
Monitoring Voluntary activity
What does rodent wheel-running activity display?
A near-24h ‘free-running’ rhythm in constant conditions
What are rodent wheel-running activity rhythms are synchronised (‘entrained’) to?
24h light dark cycles
What can Rodent wheel-running activity rhythms can adapt to?
Changes in environmental conditions e.g timing of light and dark cycle
What do Physiological and behavioural rhythms anticipate?
Changes in the environment
What 3 principals are necessary for a circadian rhythm to exist?
A pacemaker
A way to synchronise to environmental cues
Effector mechanisms
What is the main circadian clock?
Suprachiasmatic Nuclei (SCN) of the Hypothalamus
What is seen in a human
with SCN damage?
Disrupted sleep rhythms
What does the SCN exhibit?
Daily Rhythms in Metabolic Activity
What is significant about the neurons in the SCN?
Each neuron is an individual clock, contain an intracellular molecular clock
How does the SCN cells intracellular molecular clock work?
A transcriptional/translational feedback loop comprising of stimulatory elements (CLOCK/BMAL1) which drive inhibitory elements (PERIOD/CRYPTOCHROME)
Where does the SCN receive light information from?
via the retinohypothalamic Tract (RHT)
What regulates the melatonin release from the Pineal Gland?
Light and circadian signals from the SCN
What does light do to melatonin release?
Light rapidly supresses melatonin release
What does melatonin do?
Melatonin acts on receptors across the brain and body, allowing the SCN to convey time of day signals to other tissues
What does a lesioned SCN do to evolutionary fitness and mortality rates?
Lowers evolutionary fitness
Increases mortality rate
What are ultradian rhythms?
Biological rhythm with a period <24h
Give two examples of ultradian rhythms
- Growth hormone is pulsatile every 3h
- Human sleep cycles with a 90 min period.
What are Infradian rhythms?
Biological rhythm with a period >24h
Give 3 examples of infradian rhythms
- bird migration
- reproductive cycles
- hibernation
Give 2 examples of circannual rhythms
- squirrel hibernate every year
- male sheep testicles change in size depending on length of days i.e in winter they are bigger, ready to mate
How long is a circatidal rhythm?
24.8 hours
Give an example of a circatidal rhythm
Marine insect from the North Atlantic emerges from the sand and swims at high tide to feed and mate - they keep this rhythm in constant conditions
