RT Journal Article SR Electronic T1 From the Literature: A new model for the morphology of the arrector pili muscle in the follicular unit based on three-dimensional reconstruction. JF International Society of Hair Restoration Surgery FD Publication of the International Society of Hair Restoration Surgery SP 186 OP 186 DO 10.33589/16.5.0186 VO 16 IS 5 A1 Jiménez-Acosta, Francisco A1 Song, WC A1 Hwang, WJ A1 Shin, C A1 Koh, KS YR 2006 UL http://www.ISHRS-HTForum.org/content/16/5/186.abstract AB In the classic model of the arrector pili (AP) muscle, each hair follicle is independently associated with a single AP muscle. Recently, new models have been proposed based on interpretations of serial histological cross-sectional images. The purpose of this study was to confirm the morphology of the AP muscle in relation to the follicular unit (FU) using quantitative threedimensional (3D) reconstruction of serially sectioned images. Skin samples were obtained from the parietal region of the scalp, and processed using routine histological procedures. The serially sectioned slides were stained with Masson’s trichrome. All the hairs and hair follicles of the FU exhibited some degree of slanting, with the single AP muscle slanted in the same direction. The distal portion of the AP muscle was divided into branches, as in a bronchial tree. There was branching in the single AP muscle present in the FU, and it was inserted into all the hair follicles of the FU either tightly or loosely. We suggest that the classic anatomy of the AP muscle must be modified with this new model, now confirmed by computer-based 3D reconstruction.