Morphometric study of the cochlea of the rabbit (Oryctulagus cuniculus)

Abstract

A detailed morphometric study of the cochleae in four rabbits (Oryctulagus cuniculus) was made from graphic reconstructions of serial sections. Morphometric changes studied along the length of the cochlea were (i) the cross-sectional areas of the scalae vestibuli, tympani, and media, (ii) the width of the basilar membrane, (iii) the cross-sectional area and thickness of the basilar membrane, and (iv) the density of the bipolar ganglion cells innervating the organ of Corti. Changes in the cross-sectional areas of the scalae tympani and vestibuli were similar, both decrease from the cochlear base to 1.2 mm, increase to maximum values of 1.4 mm2 at 3.0 mm, and decrease to 0.4 mm2 at 4.3 mm. The cross-sectional area of the scala media remained unchanged. Three distinct morphometric changes were observed in the width and cross-sectional area of the basilar membrane. Firstly, there is a steep increase from the basal end to 3.2 mm, secondly a gradual increase from 3.2 to 8.5 mm, and thirdly, the greatest values occurred between 8.5 and 9.1 mm. The average number of bipolar ganglion cells estimated within the spiral ganglion was 26 700. The density of ganglion cells decreased from the base to 1.9 mm and then increased to its greatest density of 2800 cells/mm2 between 8.5 and 10.5 mm. The location of maximum density coincided with the location of the basilar membrane where the stiffness gradient was relatively uniform.