Ontogenetic approach to inner and outer hair cell function.

Anatomo-functional relationships made during ontogenesis seem to offer possibilities of a better understanding of cochlear function. The asymmetrical kinetics of inner and outer hair cells (IHCs and OHCs) structural development can assist in determining their functional role. Light- and electron-microscopic observations of cochlear development in kittens, guinea pigs, hamsters and rats reveal that the maturation of IHC and their afferent and efferent innervation occurs first. The OHCs develop more slowly and the pattern of their innervation changes dramatically, the last stage involving the enlargement of efferent synapses. The timing of this maturation correlates well with the development of cochlear function. The findings suggest that IHCs are required for the onset of auditory function while mature OHCs are necessary for the more discriminative properties of the cochlea.