Circadian rhythms

The biological clock is based on three synchronizers :

Melatonin, also called the “sleep hormone”, which is secreted by the pituitary gland (which gives information about the alternation of day/night) and “resets” the body with its environment.  

Light (alternation night/day) if it is received by the eye receptors in a sufficient quantity and if it is made up of good wave lengths (blue light)  

Lastly, social factors (family life, leisure, sports, etc.) also serve as synchronizers. The main circadian rhythm is the alternation of wake/sleep but other rhythms exist which vary from day to day : body temperature, our cortisol level, melatonin secretion, etc... The body also searches for a temporal balance between itself and the outside world. When our internal clock is no longer synchronized with the actual time, a pathological situation follows, of which the principal symptoms are trouble sleeping, waking up and temperament.