GLOSSARY...





biological clock---
an internal timekeeping mechanism capable of driving or coordinating a circadian rhythm.

biological rhythm---
self-sustained cyclic change in a physiological process or behavioral function of an organism that repeats at regular intervals.

circadian---
taken from Latin words meaning "around" and "day"
circadian rhythm---
a self-sustained biological rhythm which in an organism's natural environment normally has a period of approximately 24 hours

circannual---
a biological rhythm with a period of about one year

cyanobacteria---
a type of bacteria within genus Synechococcus

diurnal---
performed in or belonging to the daytime; opposite of nocturnal

eclosion---
emergence of the adult insect from its pupal case

endogenous---
self-sustained rhythm generated within an organism

entraining agent---
an environmental time cue such as light that has the ability to reset a biological clock

euthermic---
producing or creating heat or warmth

exogenous---
rhythm generated within or by an organism because of rhythmic environmental cues that are external to the organism

free running---
natural self-sustained rhythm that exists in the absence of all environmental cues. When a human is free running, his/her cycle appears to be slightly longer than 24 hours.

genome---
the total genetic content of a cell
heliotrope---
one of several species of plants whose flowers or stem buds face east in the morning, follow the movement of the sun during the day, and face west in the evening

homeotherm---
organism whose internal body temperature is maintained at a relatively constant temperature through the organism's metabolic activities; its body temperature typically does not change in response to changes in environmental temperature fluctuations; homeotherms were once called "warm-blooded"

hypothalamus---
small area of the brain near the top of the brain stem; control site of behaviors such as feeding or drinking, temperature regulation, secretion of hormones through its effect on the pituitary gland

infradian---
describes processes having periods much greater than 24 hours

melatonin---
a hormone secreted by the pineal gland used as a marker of circadian rhythmicity in humans

period---
the time that elapses before a rhuthm starts to repeat itself

photoperiodism---
the length of light in a light/dark cycle

poikilotherm---
organism whose internal body temperature varies with and remains close to environmental temperature; poikilotherms were once called "cold-blooded"

pulsatile---
rhythmic regular movement

sleep debt---
a deficit in normal sleep time

tau---
this term refers to an organism's period length

temporal---
of or relating to time

ultradian---
describes processes having periods much less than 24 hours

zeitgeber---
taken from German words meaning "time givers"; an environmental time cue such as sunlight, food, noise, or social interaction that usually helps reset the biological clock to a 24-hour day