AP PSYCHOLOGY

Detailed explanation-1: -Light directly entrains the master clock, the suprachiasmatic nucleus (SCN) which lies in the hypothalamus of the brain and is responsible for synchronizing internal rhythms. However, recent evidence underscores the importance of other hypothalamic nuclei in regulating several essential rhythmic biological functions.

Detailed explanation-2: -Circadian rhythms are regulated by small nuclei in the middle of the brain. They are called the suprachiasmatic nuclei (SCN). Nuclei act as control centers.

Detailed explanation-3: -Although circadian clocks throughout the body are synchronized in large part through the suprachiasmatic nucleus (SCN) of the hypothalamus, rhythmicity in other hypothalamic nuclei has proved to be a critical regulator of physiological rhythms such as the sleep–wake cycle and daily food intake.

Detailed explanation-4: -Via these diverse connections, the thalamus seems to make major contributions to circadian sleep regulation and wakefulness. The SCN contains specialized neurons which drive circa-dian rhythms in mammals, including humans [5, 22].