WordNet

make ones way by force; "He muscled his way into the office"
animal tissue consisting predominantly of contractile cells (同)muscular_tissue
one of the contractile organs of the body (同)musculus
authority or power or force (especially when used in a coercive way); "the senators used their muscle to get the party leader to resign"
the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...
the 16th letter of the Greek alphabet

PrepTutorEJDIC

〈U〉(動物体の組織としての)『筋肉』,筋(きん);〈C〉(体の各部を動かす)筋肉 / 〈U〉力,(特に)筋力,腕力 / 《俗に》(…に)強引に割り込む《+『in on』(『into, through』)+『名』》
〈C〉パイ(ギリシア語アルファベットの第16字Π,π;英語のP,pに相当) / 〈U〉円周率(記号はπ)
ごちゃまぜの活字 / ごちゃまぜ,混乱
《集合的に》たくさんのくい / たくさんのくいで作った物
筋肉の,筋力のある / 力ずくの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/04/30 15:12:52」(JST)

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The arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end^[1] - known colloquially as goose bumps.

Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit), and is innervated by the sympathetic branch of the autonomic nervous system. The contraction of the muscle is therefore involuntary - stresses such as cold, fear etc. may stimulate the sympathetic nervous system and thus cause contraction, but the muscle is not under conscious control.

Contraction of the muscles has a number of different purposes. Its principal function in the majority of mammals is to provide insulation: 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. Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair.

The effectiveness of the muscles' action in humans has been questioned, as humans have relatively little body hair to allow for thermal insulation.

Additional images

Base of pilosebaceous unit
Insertion of sebaceous glands into hair shaft
Cross-section of all skin layers

References

^ David H. Cormack (1 June 2001). Essential histology. Lippincott Williams & Wilkins. pp. 1–. ISBN 978-0-7817-1668-0. Retrieved 15 May 2011.

Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web; http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/hair.html
Burkitt, Young et al. (1993). Wheater's Functional Histology: a text and colour atlas. Heath. p. 162.

UpToDate Contents

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1. 脱毛の評価および診断 evaluation and diagnosis of hair loss
2. 子宮平滑筋腫（子宮筋腫）の変異型 variants of uterine leiomyomas fibroids
3. 平滑筋肉腫 cutaneous leiomyomatosis
4. 化学療法による脱毛 chemotherapy induced alopecia
5. 尿路感染症における細菌付着およびその他の病原因子 bacterial adherence and other virulence factors for urinary tract infection

English Journal

Cutaneous leiomyoma in a child: A case report.

Dilek N, Yüksel D, Sehitoğlu I, Saral Y.SourceDepartments of Dermatology, Recep Tayyip Erdoğan University Medical Faculty Hospital, Rize 53000, Turkey.
Oncology letters.Oncol Lett.2013 Apr;5(4):1163-1164. Epub 2013 Feb 15.
Leiomyoma is a benign tumour commonly encountered in the genitourinary and gastrointestinal organs in adults. Cutaneous leiomyomas are rare benign tumors arising from the arrector pili muscle of hair follicles. Cutaneous leiomyomas are more likely to occur in adults than in children. We describe a c
PMID 23599756

Responses of hair follicle-associated structures to loss of planar cell polarity signaling.

Chang H, Nathans J.SourceDepartment of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Proceedings of the National Academy of Sciences of the United States of America.Proc Natl Acad Sci U S A.2013 Mar 5;110(10):E908-17. doi: 10.1073/pnas.1301430110. Epub 2013 Feb 19.
The mammalian hair follicle unit consists of a central follicle and a series of associated structures: sebaceous glands, arrector pili muscles, Merkel cells, and sensory nerve endings. The architecture of this multicellular structure is highly polarized with respect to the body axes. Previous work h
PMID 23431170

Detailed histological structure of human hair follicle bulge region at different ages: a visible niche for nesting adult stem cells.

Wang X, Shi Y, Zhou Q, Liu X, Xu S, Lei T.SourceDepartment of Dermatology, Renmin Hospital of Wuhan University, Wuhan, China. xiongwang89@gmail.com
Journal of Huazhong University of Science and Technology. Medical sciences = Hua zhong ke ji da xue xue bao. Yi xue Ying De wen ban = Huazhong keji daxue xuebao. Yixue Yingdewen ban.J Huazhong Univ Sci Technolog Med Sci.2012 Oct;32(5):648-56. doi: 10.1007/s11596-012-1012-8. Epub 2012 Oct 18.
In the bulge region of the hair follicle, a densely and concentrically packed cell mass is encircled by the arrector pili muscle (APM), which offers a specilized microenvironment (niche) for housing heterogeneous adult stem cells. However, the detailed histological architecture and the cellular comp
PMID 23073792

Japanese Journal

Steady and Temporary Expressions of Smooth Muscle Actin in Hair, Vibrissa, Arrector Pili Muscle, and Other Hair Appendages of Developing Rats

Morioka Kiyokazu,Arai Mary,Ihara Setsunosuke
ACTA HISTOCHEMICA ET CYTOCHEMICA 44(3), 141-153, 2011
… The hair erection muscle, arrector pili, is a kind of smooth muscle located in the mammalian dermis. … The immunohistochemical study using an antibody against smooth muscle alpha actin (SMA) showed that the arrector pili muscle develops approximately 1–2 weeks after birth in dorsal and ventral skin, but thereafter they degenerate. …
NAID 130000722778

皮膚平滑筋肉腫の1例

服部友保,高橋亜由美,田村敦志,石川治
Skin cancer : official organ of the Japanese Society for Skin Cancer = 皮膚悪性腫瘍研究会機関誌 16(3), 336-339, 2001-12-28
… Cutaneous leiomyosarcoma arises from the arrector pili muscles of the hair follicle, and is a rare tumor. … Immunohistochemical studies demonstrated positivity of the tumor cells for vimentin, α-smooth muscle actin and desmin. …
NAID 10015755204