The human body undergoes daily cycles in gene expression, protein levels, enzymatic activity, and overall function. Light is the strongest regulator of the central circadian rhythm. When light strikes a mammal’s eyes, it triggers an electrical impulse that activates neurons in the suprachiasmatic nucleus (SCN), the seat of the brain’s timekeeping machinery. The SCN sets the pace for neuronal and hormonal signals that regulate body temperature, feeding behavior, rest or activity, immune cell functions, and other daily activities, which in combination with direct signals from the SCN keep the body’s peripheral organs ticking in synchrony.
© EVAN OTO/SCIENCE SOURCESunlight reaches the eyes, controls the central clock in the brain. The brain, in turn, controls different physiological processes, such as body temperature and rest-activity cycles, which then affect metabolites, hormones, the sympathetic nervous system, and other biological signals. These processes ensure that the different organ systems of the body cycle together.
Timing Treatments to the Clock
Regulated by peripheral clocks and interactions with other organs, many metabolic pathways in the body peak and ebb in specific circadian patterns. As a result, drugs targeting these pathways can work better when taken at particular times of day. Here are a few examples.
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