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]
Structure
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]
Function
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]
Thermal insulation
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.
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Journal of the American Academy of Dermatology
Volume 51, Issue 2, August 2004, Pages 217-222
The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure☆ Enrique Poblet, Francisco Ortega.
https://doi.org/10.1016/j.jaad.2004.01.054