Chronobiology: Understand the internal clock

Each of us has an internal clock that controls our biorhythm and sleep-wake patterns. Learn how the internal clock works and why it's so important for our health here.

Table of contents

1. What is the internal clock?
2. Zeitgeber of the internal clock
3. What influence does the internal clock have?
4. What influence does the internal clock have on sleep?
5. Changes in the internal clock over the course of life
6. What happens when the internal clock is disturbed?
7. Conclusion

1. What is the internal clock?

The internal clock refers to the biological system that controls the timing of our body and adapts it to a specific rhythm. It consists of a master clock, which synchronizes our 24-hour rhythm and many peripheral clocks located in the organs and tissues.

The master clock is located directly in our brain, more precisely in the suprachiasmatic nucleus (SCN), a subregion of the hypothalamus. It determines our sleep-wake cycle, controls peripheral clocks, and determines the so-called circadian rhythm, to which almost all bodily processes adapt. This rhythm is determined from birth by so-called clock genes in our cells and ensures that bodily functions are synchronized with the day-night rhythm.

However, the circadian rhythm is not precisely aligned with a 24-hour day, but actually lasts somewhat longer, namely approximately 24 hours and 11 minutes. To approximate the natural 24-hour day-night rhythm, the internal clock system must be continually regulated. This is achieved with the help of the internal clocks and their so-called zeitgebers. The most important and strongest zeitgeber is light..

2. Zeitgeber of the internal clock

Light

Light is the most important and powerful cue for our internal clocks. It is detected by special cells in our optic nerve, which send a signal to the suprachiasmatic nucleus in the brain. From there, numerous physiological processes are controlled, such as the release of certain neurotransmitters and hormones, as well as numerous metabolic activities.

Feeding times

Metabolism and nutrition are also closely linked to our body clock. The time of food intake and the composition of food can have a direct influence on our body clock. Proper meal timing can therefore also reduce the effects of jet lag when traveling across time zones.

Psychological factors (stress, worries)

Psychological stress, frequent brooding or persistent worries can also affect the internal rhythm, for example by delaying falling asleep.

Physical activity

Physical activity can also influence our body clock through its direct impact on our metabolism and numerous physiological systems. Exercise during periods of daylight can acutely promote alertness, whereas higher-intensity physical activity in the afternoon can increase sleep pressure and thus make it easier to fall asleep in the evening. Therefore, physical activity at the right time can also help improve our internal rhythm and sleep.

3. What influence does the internal clock have?

The internal clock determines numerous bodily functions. It controls the Body temperature, blood pressure, the release of hormones and neurotransmitters, as well as metabolism and the sleep-wake rhythm. This is evident, for example, in natural fluctuations during the day and night.

This allows the body to process food better at certain times or more easily compensate for blood sugar fluctuations. Before newborns become accustomed to the influence of light, food intake is the primary time cue and is closely linked to sleep.

Furthermore, the activity of individual organs is also linked to the circadian rhythm. In traditional Chinese medicine, each organ has specific working and resting times. Energy flows through the body along 12 meridians (pathways), each of which is connected to a specific organ. When a particularly large amount of energy flows through them, the organ is particularly active.

4. What influence does the internal clock have on sleep?

The body clock regulates the sleep-wake cycle and is largely oriented towards light and darkness. This means it influences when we fall asleep in the evening and when we can get up in the morning. As long as it's light, the production of the "sleep hormone" melatonin is inhibited in the brain and cells. As light exposure decreases (i.e., as darkness increases), melatonin production is reactivated, preparing the body for sleep and causing fatigue. Melatonin However, it does not make you tired, but rather prepares the body for sleep by regulating body temperature and activating cell metabolism.

This process can vary slightly from person to person, depending on light sensitivity. Therefore, chronobiology distinguishes three Chronotypes: The early, the late and the neutral types.

🌅 Early type (lark)

Early risers are usually awake early, rarely have problems with morning fatigue, and can start the day quickly. They are already physically and mentally fit in the morning. However, due to the early start to the day, fatigue sets in comparatively early in the evening.

🌇 Late type (owl)

Late risers are still productive in the evening and don't really feel tired until later in the evening. They usually reach their peak performance late in the evening and take longer to wake up and get going in the early morning. Because our social structures favor an early start to the day, evening risers in particular often have to forgo important hours of sleep because their daily routine doesn't match their natural rhythm.

⚪ Neutral types (dove)

Most people are neutral types, meaning they are neither extremely early nor very late awake.

5. Changes in the internal clock over the course of life

A person's basic temporal orientation and chronotype are already determined from birth in the clock genes. In adulthood, light is the strongest and most effective timekeeper. However, this ability must first develop in the first months of life. By about the 6th month of life, Babies a polyphasic sleep pattern – meaning they sleep in many shorter sleep phases spread throughout the day and night. Afterward, the so-called ganglion cells in the eye mature, and the children slowly adapt to the light-dependent day-night cycle.

During puberty, the chronotype may temporarily shift slightly toward the late type. However, this is completely normal, and we usually return to our original type by adulthood.

6. What happens when the internal clock is disturbed?

Disturbances of circadian rhythms are becoming increasingly common in today's society.Through shift work, traveling across time zones (jet lag) or social commitments, we often live against our natural rhythm, for example by staying up too late in the evening, having to get up too early in the morning or working at times when our internal clock is actually set for rest and sleep. This disrupts the entire biological system, which can primarily lead to sleep disorders. Many other health problems can arise, not least from disturbed sleep. That's why it's important to adapt to your own rhythm as best as possible and to prepare sufficiently for changes, such as a time change or long-distance travel.

You can find out how to get over jet lag as quickly as possible in this article.

7. Conclusion

• Chronobiology is about the temporal biorhythms of the body

• The internal clock consists of a master clock in the brain and many small clocks in the body cells and organs

• There are three chronotypes: early types, late types and neutral types

• Shift work, travel jet lag and social jet lag disrupt the internal clock and harm sleep and health