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The mystery of the superclock: How does the SCN control our biological rhythm?
The suprachiasmatic nucleus (SCN), located in the hypothalamus, is a small but powerful brain region that is primarily responsible for regulating an animal's sleep cycle. The function of this area is closely related to the intake of light. It can receive light through the photosensitive ganglion cells in the eye, thereby coordinating various physiological rhythms in the human body. However, the impact of SCN goes far beyond this. It is also involved in the regulation of many physiological functions and closely interacts with other areas of the brain.
The SCN is an important regulator of the body's circadian rhythms and is crucial for changing physiological behaviors.
The SCN is located above the optic chiasm and contains approximately 10,000 neurons, the organization of which varies between species. It consists of two nuclear clusters, called the "core" and the "shell," and there are differences in gene expression between these regions. The core region primarily responds to stimuli, while the shell region exhibits sustained gene expression, which enables the SCN to maintain stable circadian rhythms under diverse environmental conditions.
Relationship between biological rhythm and SCN
All organisms, including bacteria, plants, and animals, exhibit a nearly 24-hour circadian rhythm. Many aspects of mammalian behavior and physiology, such as sleep, physical activity, alertness, hormone levels, body temperature, etc., show distinct biological rhythms. Early studies found that when the SCN was removed, the activity rhythm of mice disappeared, proving that the existence of the SCN is essential for the generation of rhythm.
Many experiments have shown that SCN can not only generate biological rhythms, but also affect physiological responses throughout the body.
The operating principle of SCN is based on a complex molecular mechanism, in which genes such as Clock and Bmal1 are responsible for the transcription-translation negative feedback loop, driving the formation of rhythms by interacting with multiple other genes. The expression of these genes affects not only neurons within the SCN, but also "slave oscillators" in other parts of the body, making the entire physiological system coordinated.
The role of the SCN in warm-blooded and cold-blooded vertebratesWhether warm-blooded mammals or cold-blooded reptiles, their physiological behaviors are regulated by SCN. For warm-blooded animals, external temperature does not have much impact on their biological rhythms because they can maintain their physiological rhythms through a constant internal body temperature. However, for cold-blooded animals, their physiological rhythms are highly dependent on changes in ambient temperature.
The physiological behavior of cold-blooded vertebrates shows how their biological rhythms are affected by the external environment.
For example, certain reptiles (such as the Machilus sylvaticus) exhibit distinct circadian rhythms in response to temperature changes, which are related to the structure of their SCN and their dependence on the environment. These studies help us understand why different organisms have such significant differences in their circadian rhythms.
SCN and human health association
The function of SCN is not limited to regulating physiological behavior, but is also closely related to a variety of health problems. For example, irregular sleep-wake rhythm symptoms (ISWR) often occur in patients with structural damage to the SCN, and such patients are usually less responsive to light and other external stimuli, which ultimately makes sleep regularity impossible. and.
Many studies have shown that major depression is closely associated with circadian rhythm disturbances, demonstrating the importance of the SCN in emotion regulation.
In addition to depression, Alzheimer's disease (AD) patients also experience changes in SCN function, leading to disruption of biological rhythms, which can cause insomnia and other sleep disorders. The development of these diseases highlights the important role of SCN in maintaining physiological regularity and mental health.
In short, SCN is like our biological clock, regulating the body's physiological rhythms and behaviors through precise neural connections and biochemical processes. However, in today's fast-paced life, are we paying enough attention to the profound impact of this small brain area on our health?
