circadian sleep/wake cycle

Definition

Target type: biologicalprocess

The cycle from wakefulness through an orderly succession of sleep states and stages that occurs on an approximately 24 hour rhythm. [GOC:jl, http://www.sleepquest.com]

The circadian sleep/wake cycle is a fundamental biological process that governs the daily rhythms of sleep and wakefulness. It is driven by an internal biological clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus in the brain. The SCN acts as the central pacemaker, regulating the timing of physiological and behavioral processes throughout the day. The SCN receives cues from the environment, primarily light, which synchronizes the internal clock to the 24-hour day-night cycle. This synchronization is crucial for maintaining a regular sleep-wake pattern and ensuring proper functioning of various bodily systems.

The circadian clock works through a complex interplay of molecular mechanisms. A key component is the transcription and translation of specific genes that encode for proteins involved in the clock's core feedback loop. These genes are expressed rhythmically, creating a 24-hour oscillation in the levels of their respective proteins. The proteins, in turn, regulate the expression of the genes, leading to a continuous cycle.

The circadian system affects multiple physiological and behavioral processes, including:
- **Sleep-wake cycle:** The SCN regulates the release of melatonin, a hormone that promotes sleep, and other neurotransmitters involved in sleep regulation.
- **Hormone secretion:** The secretion of many hormones, including cortisol, growth hormone, and thyroid hormone, follows a circadian rhythm.
- **Body temperature:** Core body temperature fluctuates throughout the day, reaching its peak in the afternoon and its lowest point in the early morning hours.
- **Blood pressure:** Blood pressure is typically lower at night and higher during the day.
- **Digestion:** Digestive processes, including gastric emptying and enzyme secretion, are also subject to circadian regulation.
- **Cognitive performance:** Cognitive function, including alertness, memory, and attention, varies across the day.

Disruptions to the circadian clock, such as shift work, jet lag, and exposure to artificial light at night, can lead to adverse health consequences. These disruptions can increase the risk of various health problems, including sleep disorders, metabolic disorders, cardiovascular disease, and certain types of cancer.

Maintaining a regular sleep-wake cycle, minimizing exposure to artificial light at night, and engaging in other healthy behaviors can help promote optimal circadian rhythm and support overall health.'
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Proteins (1)

Compounds (3)