Biological Rhythms and Sleep Flashcards
biological rhythms
regular fluctuations in any living process
any biological process (including behaviour) that repeats itself at regular intervals
manifest at all levels of biological organization and extend across a wide frequency spectrum
ie/ hormone levels, body temperature and drug sensitivity - change over the course of the day in a repeating pattern
circadian rhythms
circa meaning lasts about a day 24 hrs
ultradian
less than 24 hours
infradian
less than 24 hours
repeats less than once a day
ie/ menstrual cycles
diurnal
active during the day
nocturnal
active at night
crepuscular
anything true of dawn/ dusk
free-running rhythms
removing light and dark
lost reaosn to tell rhythm to start or stop
rhythm runs out of phase
like a clock going slower, starting later and later everyday
in a dimly lit room - still displays biological clock.
in a constant light/ dark environment - not exactly 24 hours - varies a few mins
maintaining own personal cycle, in absense of external cues, bit more than 24 hrs long
every animal has its own clock differing from one another
endogenous clock
keeping time for animals is difficult without a watch to look at
in constant conditions they will still run at approximentally the same time each day
phase shift
resetting the clock by an external cue
entrainment
process of phase shifting, shifting a rhythm
synchronizing biological clock to a stimulus
zeitgeber
time giver; primary one in the sun (light)
entrains circardian rhythm
any cue an animal uses to sync its activity with the environment
ecological significance
awake and active to find food or away hiding from a predator
anticipation of events in an environment
evolutionary opportunity
can physically and behaviourally prepare before an event
the brains clock
normally synched to light and dark
after lesion animals were more active when the lights were out
continuously in dim light, behaviour was random, lesions eliminated the endogenous rhythm
SCN suprachiasmatic nucleus
what they landed on for the source of the brains clock
large lesions in the hypothalamus had an effect - eliminate various rhythms
above optic chiasm
shows rhythmic metabolic activity
rhythms in slices and in cell cultures
retinohypothalamic tract
carries info about light to the hypothalamus - veering out of the optic chiasm to synapse directly within SCN
some amphibians have a third eye - pineal gland is sensitive to light (has photoreceptors) helping circadian rhythm
in mammals severing optic nerve eliminates rhythm
direct projection of retinal ganglion cells to SCN via optic nerve = RHT
ganglion cells here contain specialized photopigment melanopsin
melanopsin
makes cells sensitive to light
if you are blind still get entrained through light because this in mice
- typically absent in blind humans
- have free running system
melatonin
pineal gland secretes at night
informs brain about day length
molecular foundations of the brain’s clock
- two proteins clock and cycle, bind together to form a dimer
- the clock/cycle dimer binds to DNA, enhancing the transcription of the genes for Period (Per) and Crypyochrome (Cry)
- Per and Cry bind together as a complex that inhibits the activity of the clock/cycle dimer, showing transcription of the per and cry genes, and therefore slowing production of the Per and cry proteins
- the Per and Cry proteins eventually break down, releasing clock/cycle from inhibition and allowing the cycle to start over again. the rates of gene transcription, protein complex formation, and protein degration result in a cycle that takes about 24 hours to complete
- retinal ganglion cells detect light with melanopsin and their axons in the retinohypothalamic tract release glutamate stimulation leads to increased transcription of the per gene, synchronizing (entraining) the molecular clock to the day-night cycle
circannual rhythms
seasonal cycles
for winter survival and coordinated reproduction as antipredator strategy
type 1 seasonal rhythm
endogenous/exogenous control
due to photoperiodism (melatonin duration), lesions to the SCN prevens these cycles
tract day length
type 2 seasonal rhythms
true endogenous control
SCN lesions do not affect these cycles, indicationg that there must be secondary pacemakers/ oscillators
ie/ hiberation in ground squirrels
EMG in sleep
electrode on scalp
brain potentials allow for describing levels of arousal states of sleep
eye movements and muscle tensions are also monitered in sleep
stage 1 sleep
slowing of HR
relaxation of muscles
eyes may roll slowly under eyelids
8-12 Hz
alpha rhythm - rhythm where you relax and close your eyes - time spent here decreases as drowsiness sets in
EEG has smaller amplitude and irregular frequency
stage 2 sleep
sleep spindles - characteristic of 12-14 hz where a person is said to be in stage 2 sleep. occurs in periodic bursts
K-complexes - a sharp negative EEG potential
