vilunväristysten

Vilunväristykset, commonly translated as "shivers" or "goosebumps," are a physiological reaction characterized by the sudden erection of hairs on the skin and a sensation of cold. This phenomenon is primarily caused by the activation of tiny muscles called arrector pili, which are attached to hair follicles. When these muscles contract, they pull the hair shafts upright, creating the characteristic bumpy appearance of the skin.

The contraction of arrector pili muscles is a reflex triggered by the sympathetic nervous system. This system is responsible for the body's "fight-or-flight" response. Vilunväristykset can be induced by various stimuli, including exposure to cold temperatures, sudden fright or surprise, intense emotions such as fear, awe, or even pleasure. In cold environments, the erection of hairs was historically thought to trap a layer of insulating air close to the skin, thus helping to conserve body heat. This effect is more pronounced in animals with thicker fur.

While the role in thermoregulation is less significant in modern humans due to our relative lack of body hair, the reflex persists. The sensation of coldness associated with vilunväristykset is also a part of this sympathetic nervous system response. Although the exact evolutionary purpose of retaining this reflex in humans is debated, it is understood as an involuntary reaction to certain environmental or emotional triggers mediated by the autonomic nervous system.