The amount and type of direct hair cell damaged depends
on the intensity of the sound. Above a certain minimum
of frequency and intensity, the outer hair cells show sign
of metabolic exhaustion with drooping of the stereocilia.
This correlates with the common phenomenon of temporary
threshold shift (TTS), which recovers within a few
hours. Higher sound levels damage the outer hair cell
stereocilia further, including destruction of the inter-cilial
bridges and recovery takes longer. Even higher level
sound lead to collapse of the sterocolia, and the hair cell
is eventually phagocytosed. Hair cells in the basal coil of the cochlea are the most sensitive to noise damage; they
are responsible for transducing higher frequencies and
this accounts for the high frequency hearing loss found in
noise damaged ears