Circadian cycle: biological clock, sleep-wake rhythm and sleep disturbances
The circadian cycle, also known as circadian rhythm, works as a sort of biological clock inside our body: this rather complex system determines conditions such as the sleep - wake rhythm (based on the alternation of light - dark and stimuli such as body temperature) . Let's find out together what there is to know about the circadian cycle and its rhythms, but first (if you have children) here is a video on sleep disorders in children:
So is the circadian cycle
The circadian cycle takes its name from the term coined by Franz Halberg and derived from the Latin: "circadian", in fact, comes from "circa diem", that is "around the day", precisely because it is a biological rhythm linked to a cycle. of 24 hours and in particular to the alternation between sleep and wakefulness.
The organism of living beings - and of men in particular - works on daily rhythms that organize all physical activity around a daily circadian cycle, in which the sleep phase has an extraordinary importance for the functioning of the body.
The alternation of light - dark and sleep - wakefulness influence the functioning of our body because they directly act on biological factors such as blood pressure, resistance and muscle tone, body temperature, heart rate, kidney function and more. .
The sleep-wake rhythm is particularly important in regulating the circadian cycle of each of us. It is no coincidence, in fact, that there are early risers and others who prefer to carry out most of their activities in the evening hours. Circadian rhythms can be influenced by various external parameters that lead to the alteration of the cycle, for example if you work at night that leads to sleep in the early hours of the day, or if you suffer from jet lag.
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How does the circadian cycle work?
The circadian rhythm, or circadian cycle, works quite complex. Living beings are endowed with this internal biological clock which acts thanks to at least two important structures recognized by scientists, the ascending reticular formation (FRA) and the suprachiasmatic nuclei.
The ascending reticular formation consists of a group of neurons located between the medulla oblongata and the base of the brain, and which has two different rhythms of oscillation: the first, of reduced amplitude, regulates the sleep phase and changes in the state of alert; the second, larger, regulates the alternation between sleep and wakefulness. When we fall asleep, the ascending reticular formation reduces its rhythm until it blocks the stimuli that reach the brain, thus allowing the sleep phase.
The suprachiasmatic nuclei, on the other hand, are part of the hypothalamus and regulate not only the circadian cycle of sleep-wake alternation, but also other biological rhythms such as that of hunger. They are also involved in the fundamental relationship for the circadian rhythm between the alternation of light - dark and the sleep - wake rhythm.
Circadian cycle and biological internal clock
The circadian cycle, as we have said, settles its rhythms over a period of 24 hours. According to scholars Jeffrey C. Hall, Michael Rosbash and Michael W. Young (winners of the 2017 Nobel Prize in Medicine and Physiology), this biological clock inside our body ideally divides the day into three-hour cycles, during which the body is led to perform certain activities instead of others.
The first three-hour cycle is the one that starts in the early hours of the morning: it goes from 6 to 9 am. In this cycle, the body gets back into motion little by little, ceasing the production of melatonin ( regulates the sleep phase) and bringing us to a state of alert. Between 9 and 12, however, the second cycle takes place, in which cortisol reaches its peak, as well as the activation of our body: it is the best time to carry out the most demanding activity of our day, that which requires more concentration, and sleeping is not recommended.
The third cycle that characterizes the circadian rhythm is the one that goes from 12 to 15: in this phase a bit of sleepiness returns, and it is the best time to take a short siesta or a digestive walk. Between 15 and 18, instead , it is recommended to carry out physical activity: our body temperature, in fact, increases in this phase and the heart and lungs are in top form. Physical activity, moreover, in this cycle does not interfere with sleep.
Between 6 pm and 9 pm it is good to have dinner, but without getting too heavy so as not to burden the sleep phase. Between 9 pm and midnight, the body begins to produce melatonin, the body temperature drops: it is time to go to sleep and avoid physical activity or stressful activities. The last cycle, the one between 3 and 6 in the morning, it should be absolutely dedicated to the sleep phase.
What are the sleep disorders related to the circadian cycle?
The alternation between sleep and wakefulness is fundamental for our well-being: if the circadian rhythm is altered, one can suffer from more or less serious sleep disorders, which can lead to fatigue, concentration problems, difficulties in social life.
Among the most common sleep disorders we find the so-called "delayed sleep phase syndrome", in which there are difficulties in "falling asleep and waking up, instead, at conventional times; the" early sleep phase syndrome ", in which - on the contrary - one anticipates the time of falling asleep by waking up early in the morning (it is very common in the elderly); the "jet lag syndrome", due to the change of time zone following a long journey.
For further scientific information on the circadian cycle, you can consult the website of the Veronesi Foundation.
