Figure 66.

Lin et al.⁴²⁰ study of the composite calcite crystals of otoconia. A guinea pig utricle (the vertebrate gravity receptor organ) was treated with a freeze-fracture and deep-etch procedure to examine the fibrous network and interconnections with the otoconia crystals. (a) Numerous, barrel-shaped otoconia are embedded in a loose filament matrix. Bar = 1 μm. In other images (not shown here), the otoconia appear to be linked together by filamentous cross-links. (b) Freeze fracture of an individual otoconium shows an organic central core (CO) formed by a tight meshwork of filaments, and a well-faceted, dense crystalline outer shell (OS) of calcite. Bar = 0.5 μm. (c) On the surface of the otoconia, pore-like openings can be seen in the mineral (arrows ), which appear near or under the surface filaments. Bar = 0.1 μm. (d) The fracture plane through the mineralized outer shell of this otoconium shows several deep radial channels (arrows) that seem to connect the central core with the otoconium’s outer surface. Bar = 0.2 μm. (Reprinted with permission from ref 420. Copyright 2000 Academic Press.).