Fig 2.
Fine structural features of the inner core of mammalian otoconia demonstrated by EM techniques. (a) Freeze-etching and (b) ultra-thin sectioning TEM; (b) images of the interface between inner core (IC) and outer cortex (OC) of otoconia. The freeze-etch image (a) demonstrates a rather abrupt border, but the ultra-thin section in (b) indicates that the fibrillar meshwork of the central core is continuous with the matrix of the outer cortex. The small dark plaques (arrowheads) in the cortex correspond to crystallites in the Bragg diffraction mode; (c) cross-section of otoconium showing electron-dense spots in inner core corresponding to mineralized matrix (arrowheads); (d) EDTA-treated otoconium showing several canals traversing outer cortex, connecting otoconial surface with inner core; (e) deep-etch image of freeze-fractured guinea pig otoconium showing the dense fibrillar web of inner core and innermost region of cortex. Inset: detail of area indicated by arrow showing typical hexagonal arrangement of fibrils; (f) high magnification of inner core of guinea pig otoconium showing several rows of co-aligned polygonal formations (arrows). Bars = 0.2 μm for (a) and (b); 0.3 μm (c); 0.5 μm (d); 0.2 μm (e) and 0.08 μm (inset); 0.1 μm (f).