Context: The rhythm is linked to the light–dark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a free-running rhythm. Their sleep cycle is pushed back or forward each "day", depending on whether their "day", their endogenous period, is shorter or longer than 24 hours. The environmental cues that reset the rhythms each day are called zeitgebers (from the German, "time-givers"). Totally blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Although they lack image-forming eyes, their photoreceptors (which detect light) are still functional; they do surface periodically as well.[page needed]

Question: To what is the circadian rhythm tied?
Answer: light–dark cycle

Question: What conditions will produce a free-running rhythm in humans?
Answer: total darkness

Question: What are the environmental factors that can change the rhythm?
Answer: zeitgebers

Question: What do blind mole rats have in place of vision?
Answer: photoreceptors

Question: What cycle is seperate from the circadian rythem?
Answer: Unanswerable

Question: What does total light cause in humans?
Answer: Unanswerable

Question: What is the term for the environmental cues that dertermine daily rythems?
Answer: Unanswerable

Question: What kind of mammals need external stimuli to maintain their endogenous clock?
Answer: Unanswerable