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Examples include circannual or annual cycles that govern migration or reproduction cycles in many plants and animals, or the human menstrual cycle. Ultradian rhythms , which are cycles shorter than 24 hours, such as the 90-minute REM cycle , the 4-hour nasal cycle , or the 3-hour cycle of growth hormone production.
Overview, including some physiological parameters, of the human circadian rhythm ("biological clock"). Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. [1] These cycles are known as biological rhythms.
Phase response curves for light and for melatonin administration. In humans and animals, there is a regulatory system that governs the phase relationship of an organism's internal circadian clock to a regular periodicity in the external environment (usually governed by the solar day).
A circadian rhythm (/ s ər ˈ k eɪ d i ə n /), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., endogenous ) and responds to the environment (is entrained by the environment).
An example is the interaction between circadian rhythms and environmental cues, such as light and temperature. Entrainment helps organisms adapt their bodily processes according to the timing of a changing environment. [1] For example, entrainment is manifested during travel between time zones, hence why humans experience jet lag.
The authors first fostered larvae under various constant photoperiods at a constant temperature of 20°C to determine if there was a critical duration of the photophase that affected the phase of circannual rhythm. Secondly, they examined if a decrease in temperature caused a phase-shift in the circannual rhythm.
In vertebrates, the master circadian clock is contained within the suprachiasmatic nucleus (SCN), a bilateral nerve cluster of about 20,000 neurons. [10] [11] The SCN itself is located in the hypothalamus, a small region of the brain situated directly above the optic chiasm, where it receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract.
An actogram's period shows an organism's activity rhythm in light or dark conditions. An organism's phase can be influenced by external stimuli, either causing an advance or delay in their period or not affecting it. These period changes are called phase shifts and are the main focus of PRCs. The y-axis of the PRC is the phase shift in hours ...