An excess of noise leads to an excess release of glutamate at the IHC synapse. This excess of glutamate induces excitotoxicity: first a swelling, then a disruption of the postsynaptic ending. The synapse between the IHC and the auditory nerveno longer functions (sudden deafness).
Because of neural plasticity, there may be regrowth of the dendritic ending and thus repair of the synapse, resulting in a functional recovery.
However, in the case of repetitive injuries, the neurone itself may die (see: delayed phase).