The awakening depends on the variation of the length of the days and on the increase of the external temperature; each species has a critical temperature of awakening, which reflects the environmental conditions (local climate and humidity).
(Bestial sleeps: when animals sleep)
The awakening lasts from 1 to 6 hours and generally takes place in two phases: the first, called "thermogenesis without shiver", consists in heating and supplying the chest, head, heart, vertebral column and brain with "burning" the fat reserves accumulated in the adipose tissue present in the neck and shoulder area.
The second, the "thermogenesis with shiver", is used to warm the whole body generating muscle chills through the secretion of hormones (corticosteroids produced by the adrenal glands and insulin secreted by the pancreas), which accelerate the awakening.
Chills, involuntary muscle contractions that do not produce movement but heat, in fact, are the natural "remedy" to keep the body temperature constant at low temperatures.
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