Cochlear axon calibres are adjusted to characteristic frequencies.

This study explores factors determining axon calibres, using the normal cochlear nerve as a model. The topographic distribution of axon calibres in the cochlear nerve of the guinea pig was found to correspond to its known tonotopic organization. Axons derived from the cochlear apex which carry sounds of low pitch were located centrally in the nerve and were about half as thick as axons derived from the basal turns, which are located at the periphery and carry sounds of high pitch. Intermediate ranges were located in between. If one compares these measurements with physiological data one finds axon calibres matched to characteristic frequency ranges to a degree that should cause mismatching of conduction time.