Inner hair cells (IHCs) are the center for mechanoelectrical transduction (MET) to convert sound vibration to electrical signals. Potassium ions incorporated from the stereocilia depolarize IHCs and this depolarization of the IHCs causes the subsequent activation of the voltage-dependent calcium channels CaV1.3, resulting in Ca2+ ion incorporation from the basolateral end of IHCs. The ribbon synapse is a unique component observed in IHCs and photoreceptor cells of the retina. In IHCs, the ribbon synapse is located at the basolateral region, which is composed of thousands of vesicles. This multivesicular component functions as a substantial reservoir of the neurotransmitter glutamate. The rapid, multiple vesicular exocytosis of the ribbon synapse at a level that corresponds to the intensity of the sound ensures the broad dynamic range of IHC sound sensing. Otoferlin, which is encoded by OTOF, is recognized as a critical component of the calcium-dependent exocytosis process. Patients with pathogenic variants in OTOF have hearing loss (DFNB9) and auditory neuropathy due to impaired exocytosis from IHCs. Vesicular glutamate transporter 3 (encoded by SLC17A8) plays an important role in accumulating glutamate into the synaptic vesicles, and a defect in this function is known to cause non-syndromic hearing loss (DFNA25) and auditory neuropathy. In addition, several genes, including PJVK (DFNB59), OPA1, and DIAPH3, have been reported to be associated with non-syndromic hearing loss and auditory neuropathy.