Fill in the blanks with the missing terms. Anthony participated in a sleep research study in which he spent two months in a laboratory isolated from sunlight and other natural light/dark cues. Eventually, his body clock drifted to a ______ - hour daily cycle.

The sleep-wake cycle is a fundamental concept that helps us to comprehend how our bodies regulate sleep and wakefulness over a 24-hour period. Imagine it as a daily rhythm that signals our body when to feel alert and when to wind down for the night. This cycle is largely dictated by an internal process known as the circadian rhythm, which works like an internal master clock orchestrating various physiological processes.

For a proper understanding, we need to be aware that a myriad of factors influence this cycle including sunlight exposure, daily schedules, and even our meal times. When functioning optimally, it gears us up each morning as we are exposed to light and then gradually prepares us for sleep when darkness sets in. This natural cycle ensures that we sustain a balance of rest and activity that is vital for our overall well-being. There are times when our sleep-wake cycle may be disrupted due to factors like jet lag or shift work, resulting in what some refer to as sleep disorders.

The internal clock, also known as the circadian clock, resides within our brain and is primarily located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN takes its cues from environmental factors, predominantly light, to regulate a host of bodily functions including the sleep-wake cycle, hormone release, and even body temperature.

In essence, our internal clock works on a roughly 24-hour schedule which aligns with the earth's day-night cycle. However, without the typical synchronizing agents such as the rise and set of the sun, our internal clock can become misaligned. This is what transpires during isolation from natural light and dark cues; the circadian rhythm can begin to free run, often extending beyond the traditional 24-hour cycle. This change indicates not just the flexibility but also the sensitivity of our internal time-keeping system to the external environment.

Light and dark cues are critical moderators of our circadian rhythm. The presence of sunlight or the absence thereof sends potent signals to our brain concerning the time of day, thus regulating our internal clock. During the day, light exposure encourages alertness and energy, thus promoting wakefulness, while darkness triggers the secretion of melatonin, a hormone that prepares our body for sleep.

Researchers have discovered that prolonged exposure to artificial light and frequent use of electronic devices before bedtime can interrupt the natural initiation of sleep. People living in regions with extended daylight hours or those who work night shifts also typically experience challenges with their sleep-wake cycle. Understanding the impact of light and dark on our internal clock can empower us to make lifestyle adjustments to foster healthier sleep patterns and overall circadian health.