You may be encountering the term "circadian rhythm" for the first time, though you’ve likely heard of it before as the "biological clock." One of the most evident manifestations of this rhythm occurs after the month of Ramadan, when you may find it difficult to regulate your sleep schedule. You might experience moments when your body demands sleep, and you feel unable to resist that need. Perhaps you've even wondered why you tend to feel sleepy or wake up at roughly the same times every day, even without an alarm. The reason lies in the presence of an internal biological clock within your body that performs the function of regulating and alerting these physiological cycles. The internal clock in the body regulates circadian rhythms, which encompass physical, behavioral, and mental changes that follow a roughly 24-hour cycle. These rhythms primarily respond to light and darkness in the organism’s surrounding environment. The circadian rhythm, or daily cycle, is a natural internal clock that regulates the sleep-wake cycle and repeats approximately every 24 hours. Various body systems follow circadian rhythms that are synchronized with a master clock located in the brain. This master clock is directly influenced by environmental cues, particularly light, that is why circadian rhythms are closely linked to the cycle of day and night. Studies have shown that the circadian rhythm can also be influenced by other factors such as ambient temperature, meal timing, stress, and physical activity. The master biological clock is located in the brain and is composed of thousands of neurons that help synchronize the body’s functions and activities. In other words, it regulates bodily processes at specific times, such as those that follow a 24-hour cycle—like sleep and wakefulness—as well as functions that extend beyond 24 hours, such as the menstrual cycle in women. In addition to controlling sleep and wake cycles, the internal clock also regulates other vital functions throughout the day, including body temperature, immune system activity, and the timing of hunger. Many individuals observe a natural variation in their sleep and wake times, as well as in their alertness levels throughout the day. The regulation of sleep is governed by two primary systems: the sleep/wake homeostasis and the circadian biological clock. The sleep/wake homeostasis system signals the body when it needs to sleep after staying awake for an extended period. It also helps ensure that the body gets sufficient rest throughout the night to compensate for the hours spent awake. In contrast, the biological clock regulates the timing of sleepiness and alertness throughout the day. The circadian rhythm naturally fluctuates, with peaks and dips at different times during the day. The biological clock also promotes alertness at specific times of the day, even if a person has had extended hours of sleep. During adolescence, certain changes occur in the circadian rhythm, and most teenagers experience a delay in sleep timing. This shift in the circadian cycle causes adolescents to naturally feel alert later at night, making it difficult for them to fall asleep before 11:00 p.m. The biological clock is regulated by a part of the brain called the suprachiasmatic nucleus (SCN)—a cluster of neurons located in the hypothalamus that responds to light and dark signals. Light enters the eye and is transmitted to the SCN via the optic nerve, signaling the internal clock that it is time to wake up. The SCN also sends signals to other parts of the brain that control hormone production, body temperature, and other functions that influence our feelings of sleepiness or alertness. For example, in the morning, upon exposure to light, the SCN triggers processes such as raising body temperature, stimulating the release of hormones like cortisol, and delaying the release of melatonin—a hormone associated with the onset of sleep and typically produced when it gets dark. Melatonin levels rise in the evening and remain elevated throughout the night, thereby promoting and maintaining sleep. At this point, I would like to clarify to the reader that in adolescents, melatonin levels in the blood naturally rise later at night compared to other age groups. As a result, they may find it difficult to fall asleep early. To help teenagers get enough sleep, it is recommended to keep lighting dim in the evening as bedtime approaches and to expose them to bright light in the early morning hours. The biological clock rhythm plays a crucial role in regulating the sleep-wake cycle. It controls the production of melatonin, a hormone that promotes sleep, which rises in the evening (inducing the feeling of drowsiness) and decreases in the morning. Disruptions in this rhythm can lead to difficulties in falling asleep, maintaining sleep, or waking up. Various factors can disrupt the rhythms of the biological clock. These include exposure to light during the night (including the use of electronic devices), shift work, travel across time zones (resulting in jet lag), certain medications, and lifestyle factors such as irregular sleep and eating patterns. Aging and some health conditions may also disrupt the biological clock rhythm. Resetting your circadian rhythm involves establishing a regular sleep schedule and exposing yourself to natural light during the day while minimizing light exposure at night. Regular physical activity, consistent meal times, and reducing caffeine intake can also help. In some cases, doctors may recommend light therapy, melatonin supplements, or other treatments. Signs that your circadian rhythm may be disrupted include difficulty falling asleep or waking up, daytime fatigue, and staying awake and alert late at night. Other symptoms may include changes in appetite or digestion, mood fluctuations, and difficulty concentrating or remembering. In conclusion, dear reader, you should take care of your health, which is closely linked to the biological clock. Always remember that a sound mind resides in a sound body, which governs the regulation of its biological clock.