Circadian clocks are the central mechanisms that drive circadian rhythms. Dynorphins are important in maintaining homeostasis through appetite control and circadian rhythms. There are two separate processes related to biological timing&colon; circadian oscillators and homeostasis. Inputs from suprachiasmatic nucleus about levels of lighting (circadian rhythms). The photic response is likely linked to effects of light on circadian rhythms. A disruption of the circadian rhythm would therefore generate sleep disturbances. Preliminary research indicates that ghrelin participates in the regulation of circadian rhythms. The internal circadian clock promotes sleep daily at night. These variants occur near genes known to be important in photoreception and circadian rhythms. It is responsible for controlling circadian rhythms. Melanopsin serves an important role in the photoentrainment of circadian rhythms in mammals. Their circadian rhythm stays intact during hibernation. Light is an environmental stimulus for regulating circadian cycles. There may also be some changes in circadian rhythms. This suggests that "Clk" contributes to the amplitude of circadian rhythms.