Zeitgebers such as light have what effect on circadian rhythms?

Zeitgebers such as light have what effect on circadian rhythms?

• A. They slow circadian cycles
• B. They have no effect on circadian rhythms
• C. They only influence metabolic rate
• D. Zeitgebers like light reset and synchronize circadian rhythms with day-night cycles

Answer: (D)

External cues like light act as timing signals that adjust our internal clock. The circadian system runs on roughly a 24-hour cycle, generated by clock genes in the brain’s suprachiasmatic nucleus, but it needs daily cues to stay aligned with the external day-night environment. Light is the main zeitgeber because it reaches the retina and activates specialized cells that send signals to the SCN via the retinohypothalamic pathway. This input resets the clock each day, a process called entrainment, so the timing of sleep, alertness, hormone release, and body temperature stays synchronized with day and night. Morning light tends to advance the clock, while evening light tends to delay it, helping maintain a stable 24-hour rhythm. In short, zeitgebers like light reset and synchronize circadian rhythms with day-night cycles.

External cues like light act as timing signals that adjust our internal clock. The circadian system runs on roughly a 24-hour cycle, generated by clock genes in the brain’s suprachiasmatic nucleus, but it needs daily cues to stay aligned with the external day-night environment. Light is the main zeitgeber because it reaches the retina and activates specialized cells that send signals to the SCN via the retinohypothalamic pathway. This input resets the clock each day, a process called entrainment, so the timing of sleep, alertness, hormone release, and body temperature stays synchronized with day and night. Morning light tends to advance the clock, while evening light tends to delay it, helping maintain a stable 24-hour rhythm. In short, zeitgebers like light reset and synchronize circadian rhythms with day-night cycles.