A higher magnification of one of the semicircular canals and of the crista ampullaris (CA) within the canal seen in the lower right of Figure l is provided here. The receptor for movement, the crista ampullaris (note its relationships in Fig. 1), is present in each of the semicircular canals. The epithelial (EP) surface of the crista consists of two cell types, sustentacular (supporting) cells and hair (receptor) cells. (Two types of hair cells are distinguished with the electron microscope.) It is difficult to identify the hair and sustentacular cells on the basis of specific characteristics;
they can, however, be distinguished on the basis of location (see inset), as the hair cells (HC) are situated in a more superficial location than the sustentacular cells (SC). A gelatinous mass, the cupula (Cu), surmounts the epithelium of the crista ampullaris. Each receptor cell sends a hair-like projection deep into the substance of the cupula.
The epithelium rests on a loose, cellular connective tissue (CT) that also contains the nerve fibers associated with the receptor cells. The nerve fibers are difficult to identify because they are not organized into a discrete bundle.
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