Arrector pili muscle: evidence of proximal attachment variant in terminal follicles of the scalp.

Abstract

There is general agreement that the proximal attachment site of the arrector pili (AP) muscle, via elastic tendons, is the bulge region, where follicular stem cells are situated. A variant of this insertion, in which the AP muscle surrounds the follicle circumference, has been described in human facial vellus hair follicles. To investigate whether terminal hair follicles of the human scalp may also present this variant of proximal insertion of the AP muscle. Histological and immunohistochemical methods were used. At the bulge level, bundles of the AP muscle were seen to encircle the entire hair follicle. Terminal follicles of the human scalp may also present this variant of proximal insertion of the AP muscle.