Figure 1.

Vestibular hair cells of the utricle and saccule are organized within the inner ear to optimize the detection of linear accelerations in all directions. A, The vestibular hair cells within the utricle and saccule facilitate the detection of horizontal (utricle) and gravitational accelerations (saccule). In addition, hair cells within the ampullas of the semicircular canals detect rotational movements. Auditory hair cells detect sound and are located within the cochlea. B, In the utricular and saccular epithelia the adjacent hair cells share a similar polarity (small arrows) and are organized about a line of reversal (red dashed line) that separates lateral and medial domains (light gray shading). Arrows indicate the functional and morphological polarity of the bundle and are drawn from the shortest stereocilia to the kinocilium. C, The stereocilia bundle of an individual hair cell is arranged in a staircase manner, with the tallest stereocilia adjacent to the kinocilium. Deflections of the bundle toward the kinocilium are excitatory. D, Polarity can be visualized by using phalloidin (red) and an antibody against acetylated tubulin (green) to label the stereocilia and kinocilia, respectively. E, Alternatively, polarity can be visualized by using α-spectrin antibodies (red) to label the cuticular plate. Pericentrin immunolabeling (green) corresponds to the basal body beneath the kinocilium. E′, Via visualization with α-spectrin alone, the insertion point of the kinocilium and corresponding orientation of a hair cell can be determined by the position of a void of immunofluorescent labeling (arrowhead). Scale bars, 5 μm.