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The Role of the Audiologist in Life Care Planning
Published in Roger O. Weed, Debra E. Berens, Life Care Planning and Case Management Handbook, 2018
William D. Mustain, Carolyn Wiles Higdon
OAEs are acoustic signals generated by the inner ear of healthy ears in normal-hearing individuals. The acoustic signals are by-products of the activity of the outer hair cells in the cochlea. The clinical significance is that they are evidence of a vital sensory process arising in the cochlea, and OAEs only occur in a normal cochlea with normal hearing.
Special Senses
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Kenneth A. Schafer, Oliver C. Turner, Richard A. Altschuler
The hair cells are most often implicated in auditory disorders (including genetic and aging) or trauma from stresses such as drugs and noise. In mammals, there is no regeneration of cochlear inner or outer hair cells after their loss. Outer hair cells are the most sensitive to disorders of the inner ear including noise, ototoxins, aging, and trauma. Hearing loss in the range of 10–50 dB is usually attributed to loss or dysfunction of the outer hair cells. The movement of outer hair cells sets up an “emission” that can be easily measured with an external recording device in the ear canal (“otoacoustic emissions”), providing a quick way to assess outer hair cell function and potential toxicity.
The ear, nose and sinuses
Published in Professor Sir Norman Williams, Professor P. Ronan O’Connell, Professor Andrew W. McCaskie, Bailey & Love's Short Practice of Surgery, 2018
Professor Sir Norman Williams, Professor P. Ronan O’Connell, Professor Andrew W. McCaskie
There are approximately 15 500 hair cells in the human cochlea. They are arranged in rows of 3500 inner and 12 000 outer hair cells. The inner hair cells act as mechanicoelectric transducers, converting the acoustic signal into an electric impulse. The outer hair cells contain contractile proteins and serve to tune the basilar membrane on which they are positioned.
The applications of targeted delivery for gene therapies in hearing loss
Published in Journal of Drug Targeting, 2023
Melissa Jones, Bozica Kovacevic, Corina Mihaela Ionescu, Susbin Raj Wagle, Christina Quintas, Elaine Y. M. Wong, Momir Mikov, Armin Mooranian, Hani Al-Salami
The sensory hair cells transduce auditory signals, with mechanosensitive stereocilia bundles positioned on their apical surface. The bundles themselves are arranged in a highly uniform chevron shape, with each bundle containing 50 to 200 stereocilia [39]. Outer hair cells contribute to the process of cochlea amplification, assisting in the selectivity and diversity of hearing via the mechanical boosting of sound-induced vibrations [44]. This offers a wide dynamic range, sharp frequency tuning and overall high sensitivity. Inner hair cells possess mechanotransduction channels, indicating their ability to result in a biological response from a physical stimulus. Which, in the case of inner hair cells, occurs via the auditory nerve fibre synaptic connection, permitting the detection of sound, and transmitting information about the acoustic environment to the central auditory system. Overall, sound vibrations are detected by inner hair cells following amplification by outer hair cells [45–47]. One key element of significance to note is the inability for the regeneration of mammalian ear hair cells. This is in contrast to non-mammalian vertebrate species which have the capacity for hair cell restoration via the regeneration of supporting cells. Hence, damage to mammalian hair cells is currently considered permanent and leads to varying degrees of hearing loss [48–50].
Experimental drugs for the prevention or treatment of sensorineural hearing loss
Published in Expert Opinion on Investigational Drugs, 2023
Judith S Kempfle, David H. Jung
Inner hair cells have the ability to transduce mechanical movements into electrical signals via fiber-like structures at the apical end, the stereocilia [12]. Ribbon synapses at the basal end of hair cells release the neurotransmitter glutamate in response to sound-evoked stereocilia motion. Afferent spiral ganglion neurons are stimulated via their α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) glutamate receptors, and the electrical signal is then propagated along the auditory pathway. Outer hair cells act in response to auditory signals and function as modulators and amplifiers of sound [13]. The protein Prestin in the membrane of outer hair cells can undergo conformational changes in response to electrical potential, and this electromotility contributes to frequency selectivity and helps to amplify the auditory signal [13]. The electrical gradient between endolymph and perilymph is maintained by the stria vascularis, which flanks the scala media and organ of Corti, and which harbors various ion pumps to restore the resting potential [14].
Distortion product otoacoustic mapping measured pre- and post-loud sound exposures
Published in International Journal of Audiology, 2022
Chris A. Brooks, Odile H. Clavier, Abigail M. Fellows, Catherine C. Rieke, Christopher E. Niemczak, Jiang Gui, Nina J. Pryor, Hilary L. Gallagher, Sara A. Murphy, Sean R. Wise, Claire Healy-Leavitt, Lindsay V. Allen, Jay C. Buckey
DPOAE amplitude maps provide a comprehensive picture of outer hair cell responses. Their use for tracking the response to hazardous noise exposure has been limited by insufficient data on the variability of the measurements without noise exposure and by a lack of reliable analysis techniques. This study has established the variability of DPOAE amplitude maps in normal hearing subjects, which provides a threshold of DPOAE variability above which map changes can be considered significant. Also, the study developed a robust approach to analysing repeated maps that provides either a single overall score or a detailed map of responses over time. The results from the noise exposure sub-studies show that the response to hazardous loud sound is not uniform across the map, and therefore across the cochlea. There was also considerable interindividual variability in the outer hair cell response to damaging sound. Significant changes were seen with the audiogram, DP-gram, and map z-scores after loud music exposures, but the map scores were a much more robust measure.