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Muscles attached to hair follicles From Wikipedia, the free encyclopedia
The arrector pili muscles, also known as hair erector muscles,[1] are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end,[2] known colloquially as goose bumps (piloerection).[3]
Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit).[4] Each is innervated by the sympathetic division of the autonomic nervous system.[4] The muscle attaches to the follicular stem cell niche in the follicular bulge,[3][4][5] splitting at their deep end to encircle the follicle.[6]
The contraction of the muscle is involuntary. Stresses such as cold, fear etc. may stimulate the sympathetic nervous system, and thus cause muscle contraction.[4]
Contraction of arrector pili muscles have a principal function in the majority of mammals of providing thermal insulation.[4] Air becomes trapped between the erect hairs, helping the animal retain heat.
Erection of the porcupine's long, thick hairs causes the animal to become more intimidating, scaring predators.[citation needed]
Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair.[7]
Arrector pili muscles also stabilise the base of the hair follicle.[5][6]
Skin conditions such as leprosy can damage arrector pili muscles, preventing their contraction.[8]
The term "arrector pili" comes from Latin. It translates to "hair erector".[1]
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