A quantitative analysis of the afferent innervation of the organ of corti in guinea pig.

A quantitative analysis of the afferent innervation of the organ of Corti was made on normal and vestibular nerve-sectioned guinea pigs. Section of the vestibular nerve at the internal auditory meatus provided an efficient means of eliminating the efferent innervation to the cochlea without significant loss of afferent fibres. Nerve counts on normal and de-efferented animals revealed that about 10-15 % of the cochlear afferent innervation supplies the outer hair cells. The remaining 85-90% of afferent fibres innervate the inner hair cells. As in cats, all tunnel spiral bundle fibres and upper tunnel crossing fibres were efferent to outer hair cells. Since unmyelinated fibres in the osseous spiral bundle were not counted, quantitative analysis of the efferent innervation to inner hair cells could not be made. However, a significant loss of myelinated fibres in the osseous spiral lamina after vestibular nerve section confirms that many myelinated efferent fibres are present in this region.