Biological Rhythms

Chronobiology

Field which studies biological clocks and biological rhythms within an organism

ultradian

(less than 24 hours) short cycles that repeat multiple times a day

circadian

(around 24 hours) daily cycles synced to light-dark cues

infradian

(more than 24 hours) often guided by day length

Circalunar

around 29.5 days

circannual

around a year

Diurnal

active during the light

Nocturnal

active during the dark

adaptive value of circadian rhythm

allow animals to anticipate predictable daily events rather than simply react to them

what are the cues from the environment

zeitgeber, phase shift, entrainment, period

zeitgeber (time-giver)

any cue that an animal uses to synchronize with the environment

Phase shift

shift in activity in response so a synchronizing stimulus, such as light

entrainment

process of shifting the rhythm to an environmental stimulus

period

time it takes for one cycle of the rhythm to occur

what is the primary zeitgeber for most mammals

light

subjective time

animal’s internal estimate of time of day

free running rhythm

a biological rhythm that continues in the absence of external time cues

what is the suprachiasmatic nucleus (SCN)

Neural basis for the endogenous

where is the SCN

Part of the hypothalamus, just above the optic chiasm

what does a SCN lesion lead to

disruptions in circadian rhythm and hormone secretion

is the SCN required for generating circadian rhythm

yes

How does light information transport in mammals

goes from the eye to the SCN via the retinohypothalamic pathway

How does the SCN detect light

Circadian rhythms entrain to light-darl cycles using different pathways depending on the species

Where does the SCN detect light in amphibians and birds

The pineal gland, as it is sensitive to light, light penetrates directly in species with thin skulls

What is melanospin

a photopigment that makes them sensitive to light, especially blue light

what are light induced phase shifts

the degree to which the clock is adjusted depends upon the timing of the exposure to light

midday subjective day

no effect
-light exposure has minimal effect

early subjective night

delays the clock
the clock was just entering the night
light at this time delays clock, delaying timing of activity or sleep

late subjective night

moves the clock forward
clock was near end of night phase
light at this time advances clock, shifting activity or sleep earlier

what are infradian rhythms

biological rhythm with a period longer than 24 hours

examples of infradian rhythms

menstrual cycle (28 days), seasonal breeding, hibernation cycles, migration timing

ultradian rhythm

biological rhythm with a period shorter than 24 hours

examples of ultradian rhythm

activity, feeding, hormone release, sleep cycles

what do free-running experiments show

animals keep a rhythm even without external day-night cues, indicating there is a endogenous clock