Circadian Rhythm Flashcards
circadian rhythm
biological rhythm with a 24hr period that persists in constant conditions
present in all organisms
benefit of the CR
survival advantage because organisms can anticipate rather than respond to environmental changes
CR functions
anticipates regular changes in the environment - tunes internal physiology to the external world
internal synchronisation (temporal organisation) - internal processes in different organs are coordinated
allow synchrony (temporal organisation) between species
examples of CRs
behavioural - sleep/wake, drinking, food
biological - glucose uptake, metabolic rate, alcohol degradation
physiological - bp, HR, pain threshold
amplitude
measures robustness of circadian period (highest to lowest period)
period
duration of one complete cycle in rhythmic variation
free running (tau)
rhythm free runs according to circadian clock H>24hrs mouse<24hrs
constant conditions, no external cues
entrainment
synchronisation of internal biological rhythms by external cues
zeitgeber
external cue
light is the primary zeitgeber
e.g. food intake/temperature
actogram
graph in CR research
vertical line = activity
exogenous vs endogenous daily rhythms
exogenous - response to change in environment by external/environmental rhythms (not internally generated)
endogenous - generated internally within the organism by a self-sustaining oscillator/biological clock (true CR)
what is the endogenous master clock
suprachiasmatic nucleus (SCN)
located at base of hypothalamus (above optic chiasm)
light perception
light detected by retina
impulses sent to SCN to entrain clock
rod and cones send signal to RGC via bipolar cells
how do RGCs detect light
melanopsin (opsin photopigment)
found in intrisically photosensitive RGCs (ipRGCs)
endoded by Opn4 gene
roles of melanopsin
light modulation of sleep
entrainment of CR
pupillary light reflex
exacerbates migraines
3 SCN inputs
1)input light pathway: retina-SCN via RHT
2)intergeniculate leaflet (IGL) innervation IGL-SCN conveys photic and non-photic info from dorsal raphe nucleus
3)DRN activated and MRN mediate entraining of arousal (non-photic)