Final answer:
Circadian rhythms are regular changes in biology or behavior that occur in a 24-hour cycle. These rhythms are controlled by the biological clock located at the base of the brain. The amount of light entering the eyes helps control the biological clock.
Step-by-step explanation:
Circadian rhythms are regular changes in biology or behavior that occur in a 24-hour cycle. In humans, for example, blood pressure and body temperature change in a regular way throughout each 24-hour day. These rhythms are controlled by a small structure called the biological clock, located at the base of the brain. The biological clock sends signals to the body that cause regular changes in behavior and body processes. The amount of light entering the eyes helps control the biological clock, which causes changes that repeat every 24 hours.
One important regulator of sleep-wake cycles in humans is the hormone melatonin, which is released by the pineal gland in response to darkness. Melatonin release is stimulated by darkness and inhibited by light. Individual differences in sleep-wake cycles, known as chronotypes, can lead to morning people or night owls, and research suggests that sleep regulation, or the brain's control of switching between sleep and wakefulness, varies between morning larks and night owls.
Disruptions in circadian rhythms can occur when people travel across time zones or work rotating shifts. Bright light therapy and exposure to bright light during working shifts, as well as dark exposure when not working, can help combat insomnia and symptoms of anxiety and depression associated with circadian disruptions.