Quick Facts
The arrector pili muscle is a type of tiny smooth muscle of the skin whose contraction causes the hair to stand erect with cutis anserina (goose flesh).
Origin: papillary layer of dermis.
Insertion: a hair follicle.
Innervation: sympathetic.
Action: elevate a hair on the skin (Dorland, 2011).
Structure/Morphology
The arrector muscles of the hair, or arrector pili, are formed by bundles of closely packed smooth muscle cells. The muscle extends obliquely attaching to the hair follicle to the papillary layer of the dermis.
At the hair follicle, the arrector pili muscle is attached to a bulged region in the connective tissue sheath via elastin fibrils. A sebaceous gland sits at the angle between the muscle and the hair follicle.
Arrector pili muscles are absent from the hairs of the face, axilla, pubis, eyelashes, eyebrows, nostrils, and external auditory meatus (Standring, 2016).
Function
When the arrector pili muscle contracts, it pulls the hair into a vertical position. It also elevates the epidermis where the hair enters and depressed the epidermis where the muscle attaches at the papillary layer of the dermis, thus forming small hillocks known as goosebumps. In addition, because of the relationship between the arrector pili muscle and the sebaceous gland at the hair follicle, its contraction aids the expulsion of the glands contents.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series: Elsevier Limited.
