Please enable JavaScript.
Coggle requires JavaScript to display documents.
Circadian Rhythms (Circadian Rhythm Basics (biological rhythms (other…
Circadian Rhythms
Circadian Rhythm Basics
biological rhythms
self sustaining
endogenous to organism
other lengths of biorhythms
ultradian
less than a day
i.e. breathing, EEG waves
infradian
many days
i.e. reproductive cycle, menstrual cycle
circannual
once a year
i.e. mating behaviors for some animals
about 24 hour period
entrained by zeitgeber (environmental cues) – usually light
free running w/ zeitgeber
hormone melatonin = secreted in 24 hours pattern w/ light as regulator
Circadian Disorders
certain brain tumors – loss of separate sleep & awake phase
elderly – advanced sleep phase syndrome
adolescence – delayed sleep phase syndrome
sometimes w/ blindness – advanced sleep phase syndrome
Sleep Control
homeostatic – sleepiness occurs after sleep debt
allostatic – mechanisms to force wakefulness or sleep
stressful situation requires staying awake
during illness, immune signals promote daytime sleepiness
over-ride normal homeostatic controls
circadian – 24-hour biological cycle
behavior & physiology oscillate w/ period of 24 hours
not noticeable because our environment also changes
travel across time zone = asynchrony
jet lag & shift work
sleep problems
gastrointestinal & metabolic problems
risk of diabetes & cardiovascular disease
Biological Clock
suprachiasmatic nucleus (SCN)
termination of retinohypothalamic tract
lesions abolish rhythm
isolated SCN still has rhythm
transplantation of SCN restores rhythm in an animal w/ SCN lesion
SCN neurons
neurons themselves = oscillators
rhythmic activity occurs in cell culture
in fetus – circadian pattern emerges b4 synapses
time keeping occurs w/ TTX (prevents action potential
Components
(light) sensory –> clock –> output to brain (behavior)
special ganglion cells express melanopsin w/ axons to SCN
rods & cones not need
Light
dominant stimulus
pacemaker = slightly inaccurate
luminosity
glutamate neurotransmitter of PGC
w/out vision –> drift – rhythm still occurs but = irregular
Pacemaker output
motor performance
memory
hormone secretion
temperature regulation
reproduction
arousal/sleep
excites orexin neurons –> inhibit VLPO
Biochemical Basis of 24 hr Rhythm
(1) clk & cyc cause per & tim mRNA to be made
(2) per & tim mRNA transported out of cell to make PER & TIM protein
(3) PER & TIM protein dimerize & length of it determines circadian rhythm
(4) dissociate & reenter nucleus to stop clk & cyc from activating more production of PER & TIM (negative feedback)
process occurs over 24 hours