Stereocilia
Stereovilli or Stereocilia is microvilli of unusual length of cilia. . * Stereocilia are unusually long, immotile microvilli that are not widely distributed among epithelia, in fact, they are (1) limited to the epididymis, to the proximal part of the ductus deferens of the male reproductive system (2) and to the sensory (hair) cells of the ear. . . * They (the Stereocilia) are included in the ear as hair cells because this unusual surface modification is treated as a separate structural entity. . . * The Stereocilia of the genital ducts are extremely long processes that extend from the apical surface of the cell and facilitate absorption. . . * Unique features: the apical cell protrusion from which they arise and thick stem portions that are interconnected by cytoplasmic bridges. . . * Like microvilli, the Stereocilia are supported by internal actin filament bundles that are cross-liked by fimbrin. But the difference is in Stereocilia, a plasma membrane-associated molecule (erzin), anchor s the actin filaments to the plasma membrane of Stereocilia. . . * The obvious differences of microvilli and Stereocilia (other than size/length and presence of erzin) is the absence of villin from the tip of the stereocilium. . . ▪️Stereocilia of the sensory epithelium of the ear are uniformed in diameter and possess an internal structure similar to that of the genital duct stereocilia but serve as sensory receptors. (Photo : aibolita.com) [source : 4th edition of Histology text an Atlas by M.H.Ross, G.I.Kaye and W. Pawlina - page 90&91]