User:Marshal MacCartney/sandbox

“Free-running period”

A free-running period is in reference to the amount of time a living organism's internal clock takes for certain cycle to reoccur without relying on any environmental stimuli. Most organisms have an endogenous clock that allows them to react to the environment or other stimuli. These clocks are usually aligned with the rising and setting of the sun, often referred to as the solar cycle or the light dark cycle. These periods, often denoted by the Greek letter τ (tau), of internally controlled circadian rhythm are what an organism perceives a normal 24-hour day is. In the brain, the superchiasmatic nucleus of the hypothalamus is the control center for an animal’s master endogenous clock even when an organism is experiencing a free-running period. Typically, individual cells and most bodily cycles align with this endogenous rhythm. Free-running periods are never completely accurate (i.e. 24 hours) and the longer they run without any environmental cues the more they will drift from a 24 hour cycle. Biological rhythms, when not cued by the environment such as an animal in constant light or constant darkness, will drift as soon as it the cycle is interrupted and in one free-running period can be off from normalcy anywhere from a few minutes to over an hour each oscillation.