This outcome has been reported following ototoxic (and neurotoxic) compounds such as trimethyltin ( Fechter and Liu 1994), hypoxia ( Brown et al. The loss in sensitivity of the CAP generated at this synapse when the CM is unchanged is consistent with dysfunction at the inner hair cell and/or type 1 spiral ganglion cell. Inner hair cells and type 1 spiral ganglion cells constitute the pre- and postsynaptic elements in the cochlea. Linda, in Comprehensive Toxicology, 2010 13.14.5 Inner Hair Cell and Type 1 Spiral Ganglion Cell Toxicity: Markers of Impairment The effect of inner hair cell loss on auditory coding at higher levels of the auditory system is as yet unknown.ī. The bottom panel shows compound action potential thresholds as a function of frequency for the same groups. The top panel shows compound action potential amplitudes for auditory nerve fibers at 8 kHz for control animals and animals subject to a single dose of carboplatin. Less severe inner hair cell loss (15–28% along the length of the cochlea) did not result in significant elevation of compound action potential thresholds, although it did lead to reduced compound action potential amplitude at higher levels. They found, like Takeno et al., that severe inner hair cell loss caused elevation of compound action potential thresholds, but that thresholds for many single auditory nerve fibers were normal, and had normal frequency tuning. (1997) examined responses from individual auditory nerve fibers following selective inner hair cell loss as well as compound action potential thresholds. (1994) found that thresholds for the compound action potential (which is a measure of neural activity in the auditory nerve) was reduced in proportion with the amount of inner hair cell loss caused by carboplatin administration. Several animal studies have investigated the effects of inner hair cell loss on auditory coding using carboplatin, which causes selective inner hair cell loss in some species. This provides the main route for transmission of information along the auditory nerve to the central auditory system. Inner hair cells synapse with type I auditory nerve fibers, and depolarization of the inner hair cells increases the probability of action potential generation in these fibers. Tip links that connect adjacent stereocilia stretch, opening cation channels and allowing potassium ions to enter the cells, causing depolarization.
Basilar membrane vibration causes stereocilia on the surface of inner hair cells to bend (see Fig. Inner hair cells transduce basilar membrane vibration into electrical activity.