CDH Paramedic Entrance Practice Exam

The circadian rhythm in humans is primarily influenced by environmental cues such as light and darkness. This biological clock is regulated by the hypothalamus, which responds to changes in light exposure. Light signals, particularly blue light from the sun, help to synchronize the body's internal clock with the external environment, promoting the sleep-wake cycle.

When light enters the eyes, it triggers a reaction in the suprachiasmatic nucleus (SCN) of the hypothalamus, which then signals the production of melatonin, a hormone that regulates sleep. During daylight, increased light levels suppress melatonin production, keeping individuals alert and awake, while darkness encourages its release, facilitating sleep.

While social interactions, physical activity, and dietary habits can also influence sleep patterns and overall health, they are secondary factors and often act within the framework of the primary influence exerted by light and darkness on circadian rhythms.