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Biological Rhythms - Coggle Diagram
Biological Rhythms
circannual
1 year; seasonal
BEHAVIOR
migratory patterns of birds; hibernation; seasonal changes in body mass
ground squirrels
weight gain, repro competence, hibernation
reflect seasonal changes in energy availability in enviro
animal is PHOTOPERIODIC if its responds (physiologically or behaviorally) to changes in
daylength
YES hamsters/sheep
NO rats/mice
info about day length is conveyed to the SCN which regulates release of melatonin from the pineal gland; SCN serves as clock and calendar
2 types
type II
truly endogenous
BW of ground squirrels that live in burrows
type I
endogenous and exogenous signals
exposure to long days is required for animal to become responsive to photoperiod again
reproduction in Syrian (golden) hamsters
photosensitive
1 more item...
photorefractoriness (how unresponsive to photoperiod) = after prolonged short days, testes spontaneously get larger and pituitary hormones increase
1 more item...
short days also lead to decreased T levels and decreased mating behaviors
critical daylength between 12 and 12.5 hours
cues that entrain
light
photoperiod; "daylength" or calendar; amt of light per 24 hour or in a light/dark cycle
that can be measured
temperature
rainfall
humidity
short v long day breeders - different effects of photoperiods on different species
short
sheep
repro stimulated by SHORT DAYS
ovulatory cycles in the fall and winter
long
syruan hamster
repro stimulated by LONG DAYS
fertile in the spring and summmer
zeitgeber
light
hamster in constant dim conditions
no zeitgeber
locomotor activity drifts - wheel running 15 min later each day
10 minutes earlier every day
not synchronized with enviro -
FREE RUNNING
get individuals with all dif free-running periods
THUS, free running periods are precise but not exactly 24 hours
that individuals not synchronized by one another's behavior AND that subtle geophysical cues are not providing any temporal info
light entrainment
light is zeitgeber
photoreceptor in eye and through retinohypothalamic tract
light info from photoreceptor from retina to...
entrains SCN pacemaker
output pathways
pacemaker has rhythm that drives "slave" oscillators
1 more item...
Intrinsically photosensitive retinal ganglion cells (ipRCGs)
contain melanopsin
encode and transmit light info directly; their axons for RHT
non image-forming
if blind, can still experience light-dark cycle
temperature
food
entrainment
phase-response curves (when light added for one hour)
largest phase DELAYS in EARLY subjective night (noct. just awoke and diurn. just retired
largest phase ADVANCES in LATE subjective night
light during subject day has no effect on noct. or diurn. animals
SCN
mammalian clock
glucose utilization (higher during day) and firing rates of SCN neurons
timing mechanism in the organism
control bio rhythm
generate rhythm (allow to occur) AND allow rhythm to be synchronized (entrained) with zeitgeber
susceptible to effects of aging
SCN volume decreases in alzheimer's patients
AND number of AVP expressing neurons in SCN are significantly lower than age-matched controls (in both senile and pre-senile)
damage disrupts daily sleep-wake cycle
DRIVES RHYTHMS
INFRADIAN - no geophysical cues
1 day; <24 hrs
ovarian/estrous cycles
hamsters - 4 days
rats - 4 or 5 days
guinea pigs and sheep - 16 days
self-sustaining; ENDOGENOUS
ULTRADIAN - no geophysical cues
1-12 hours
90min cycle of REM sleep
pulsatile secretion of GnRH, LH, T, growth hormone, corticosterone
hormones
hormones affect biological rhythms
hormones are released rhythmically
LH pulsatile release
Glucocorticoids
humans
cortisol secretion rises during sleep; highest is at waking (aka activity onset predicted)
nocturnal animals
Corticosterone cycle reversed; but peak still coincides with activity onset (when night begins)
persist in constant conditions
unless lesion SCN
gonadotropins
LH surge results from convergence of high estrogen signal from ovaries AND circadian signal from SCN
SCNx blocks daily LH pulse
LH shows rhythmic variation over time
splitting
dual control of locomotor activity and hormone release
in constant light, split activity rhythm into two separate ones that are 12 hours out of phase with each other
see if can get 2 pulses of LH if split (aka 2 peaks) - stayed 12 hours(?)
sex steroid hormones (and melatonin)
No CR of estrogens in females
CR of T in males that persists under constant conditions
CR of melatonin release
peaks during dark phase in both noct. and diurn.
shifts activity rhythms in rodents
can be used to entrain rhythms of blind humans who have become arrhythmic
LIGHT INHIBITS MELATONIN PRODUCTION
btwn SCN and pineal gland, it descends spinal cord then ascends to pineal
DURATION OF MELATONIN SECRETION DETERMINES BIOLOGICAL RESPONSE
diurnal pattern of plasma melatonin levels
melatonin levels are high at night and low during the day
seasonal variations in melatonin duration
circadian
24 hours
BEHAVIOR
parental behavior in rabbits
circadian
pups (in constant darkness in burrow) anticipate when mom comes back - emerge right before to nurse
temporal synchrony
predictable nursing rhythm exists AND pups have ability to measure time
zeitgeber is mother herself
adaptive function
prepare for predictable events
promote efficient functioning
non mammal bio clock
amphibians
parietal eyes
reptiles/birds
pineal gland
what if bio clock is disturbed?
arrhythmia - still have activity but timing is off
can rhythm be restored?
yes - donor will adopt period of the donor's rhythm - if donor is 24 hours, then will be 24 hours
tau mutant
autosomal recessive trait
running four hours earlier every day
20 hours
tau mutant+wild type = 22 hours
scn tissue alone (after scn lesion [aka made arrhythmic]) added but did not restore rhythm
genetics
clock mutant - Per gene produces PER protein
normal flies: locomotor activity rhythm of 24 hours
perS (short period) tau=19hrs
perL (long period) tau=29hrs
per0 mutant was arrhythmic
2 types of output from SCN
humoral
diffusible signal responsible for locomotor actiivty rhythms
neural
mediate neuroendocrine function
scn governs peripheral tissues rhythms in mammals
central and peripheral oscillators show different phase relationships
endogenous or exogenous?
isolation experiment
synchronized by environment; but not driven by environment