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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 sensorineural region of the semicircular canals is located in a swelling called the ampulla, in a “hill-like” convex portion called the cristae. The hair cells in this cristae ampullaris are oriented so that their tallest row faces the same direction. The stereocilia are embedded in an overlying gelatinous mass called the cupula. Angular movement of the head results in movement of the endolymph in the opposite direction. The movement of the endolymph moves the cupula, and all the hair cell stereocilia will then move in this same direction. Stereocilia are oriented so that movement of the cupula will be in an excitatory direction on one side of the head and in an inhibitory direction on the other side.
Anatomy of the Cochlea and Vestibular System: Relating Ultrastructure to Function
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
The hair bundle is composed of rows of stereocilia that increase in height in one particular direction across the apical surface of the hair cell, and a single kinocilium located behind the row of longest stereocilia (Figures 47.5a and 47.6a), but which is absent from the hair bundles of mature hair cells in the cochlea (Figure 47.5b). Stereocilia are really giant microvilli, plasma membrane-bound projections from the apical surface of the hair cell that enclose a packed array of filaments of the cytoskeletal protein, actin2–4 (Figure 47.5d–f). The kinocilium is composed of microtubules similar in form to motile cilia but they are not motile.5 In cochlear hair cells, the kinocilium is present only during development, reducing down as the cochlea matures to remain only as the basal body in the apical cytoplasm at one side of the stereociliary bundle (Figure 47.5c).6 The position of the kinocilium (or the basal body) and the longest row of stereocilia define the polarity of the asymmetric hair bundle (Figures 47.3f, 47.4d,e and 47.5a,b). Deflection of the stereocilia towards the longest ones opens MET channels, K+ enters and the hair cell becomes depolarized. Deflection in the opposite direction closes the transducer channels and the hair cell becomes hyperpolarized. The transducer channels are located at the tips of the stereocilia of the shorter rows but not in the longest stereocilia.7
Restoration: Nanotechnology in Tissue Replacement and Prosthetics
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
The stereocilia are linked in a complex network, with an inner and outer layer. The cochlea contains about 28,000 hair cells in humans. The absolute number of cells does not directly relate to auditory acuity: cats have 39,000; bats, rats, and dolphins about 15,000. In human, the interior linear extent of the cochlea is about 3.5 cm. So the density of sense cells is about 800 per millimeter (spaced at about 1.25 μm along the cochlea).
The role of serum osmolality in Meniere’s disease with acute sensorineural hearing loss
Published in International Journal of Audiology, 2023
One possible aetiology is that cochlear hair cells were damaged by potassium intoxication after Meniere’s attack (Schuknecht 1986; Merchant, Rauch, and Nadol, 1995). Additionally, recent studies have added insight into the tectorial membrane that defective proteins otogelin and alpha-tectorin cause fragile tectorial membrane, leading to a severe perturbation of endolymph and loss of interaction between the tectorial membrane and stereocilia (Roman-Naranjo et al., 2020). Temporal bone histopathological study also demonstrated severe cochlear hydrops combined with atrophied tectorial membrane incorporated into cells of the organ of Corti in an MD donor (Schuknecht and Gulya 1983). Hence, this histopathological finding further supports that impaired interaction between the tectorial membrane and stereocilia may induce hearing deterioration.
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].
Drug development for noise-induced hearing loss
Published in Expert Opinion on Drug Discovery, 2020
Isabel Varela-Nieto, Silvia Murillo-Cuesta, Miryam Calvino, Rafael Cediel, Luis Lassaletta
Mechanical injury to the hair bundle is also a key contributor to NIHL. Studies in rodents have confirmed that the disarray, fusion, or loss of stereocilia can, by itself, cause severe hearing impairment without evident HC loss [48]. Moreover, HC can survive with altered stereocilia long after noise exposure. Administration of neurotrophic factors such as NGF, and the overexpression of transcription factor Atoh1 [89] are therapeutic approaches that could contribute to restoring hair bundles and hearing recovery. More recently, the essential role of synaptic connections between HC and nerve fibers has been described in NIHL. These synapses are especially sensitive to noise injury and disappear immediately after exposure, whilst neuronal bodies and fibers, and HC could remain intact for years, leading to a hidden HL, characterized by a decrease in ABR wave I amplitude [50].