The pathology of cochlear sensory cells has been studied by light microscopy, phase contrast microscopy and transmission electron microscopy, but the study on the acoustic trauma of the sensory hairs are seldom. With guinea pigs exposed to pure tone of 500-4, 000Hz and white noise (80-135dB SPL) for 1-4 hours the damage of the cochlear sensory hairs was studied by scanning electron microscopy. The results are summarized as follows.
The sensory hair damage such as bleb formation, derangement of sensory hairs, break-off of hair tips, fusion and loss of sensory hairs due to intense auditory stimulation appeared markedly at an early stage.
The site of the most marked hair damage coincided with the response area of respective frequency in the case exposed to pure tone, namely, when exposed to 4, 000Hz it was found at the lower portion of the second turn, with 2, 000Hz at the middle of the second turn, with 1, 000Hz at the lower part of the third turn, and with 500Hz at the middle of the third turn.
Some difference could be observed in the hair damage pattern of different rows, i.e. when exposed to 4, 000Hz or 2, 000Hz, the damage was remarkable in the inner row hair cells such as the inner hair cells and the first row outer hair cells, and when exposed 1, 000Hz or 500Hz, the damage to the outer row hair cells such as the third outer hair cells was striking, namely, there was difference in the hair cell damage patterns: one when exposed to the frequencies over 2, 000Hz and the other below 1, 000Hz.
In the case exposed to white noise the center of the damage located in the lower part of the second turn coinciding to the 4, 000Hz response area, where the greater was the damage in the inner row hair cells, showing the damage pattern similar to that at 4, 000Hz.
