{"id":173,"date":"2021-05-17T14:36:05","date_gmt":"2021-05-17T05:36:05","guid":{"rendered":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/?post_type=research-content&p=173"},"modified":"2026-02-26T12:44:29","modified_gmt":"2026-02-26T03:44:29","slug":"cochlea-and-hearing-loss-1","status":"publish","type":"research-content","link":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/research-content\/cochlea-and-hearing-loss-1\/","title":{"rendered":"Cochlea and Hearing Loss"},"content":{"rendered":"\n

\u2776 Nanoscale Vibrations in Cochlear Sensory Epithelium<\/strong><\/p>\n\n\n\n

\u3010Outline of the Research Project<\/strong>\u3011<\/strong><\/p>\n\n\n\n

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The cochlea of the inner ear has the sensory epithelium, an essential tissue made up of three layers, i.e., hair-cell layer, supporting-cell layer, and extracellular matrix layer called the \u2018basilar membrane\u2019 (Fig. 1<\/mark>). Acoustic inputs firstly stimulate the basilar membrane and vibrates the sensory epithelium.  This event deflects the stereocilia of the hair cells and further activates \u2018mechanoelectrical transduction channels\u2019 at their tips. The channel\u2019s opening enters K+<\/sup> in the endolymph into the hair cells and electrically excites them. In this process, mechanical energy of sounds is transduced to electrical signals<\/strong><\/strong>. For the details of the process, see the section <\/strong>\u2018How Does the Cochlea of the Inner Ear Work?<\/a><\/strong>\u2019<\/span><\/p>\n\n\n\n

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Figure 1\u3000Sensory epithelium<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Our hearing can enhance small sounds and perceive them with higher sensitivity, whereas it detects loud sounds with lower sensitivity. This property emerges primarily from a unique pattern of the motion in the sensory epithelium. Figure 2<\/mark> plots the amplitude of epithelium\u2019s vibration as a function of intensity of the acoustic stimuli. The relationship described in this panel clearly represents the aforementioned property. This is referred to as \u2018nonlinear response\u2019<\/strong><\/strong> or \u2018nonlinear amplification\u2019<\/strong>, which disappears when the animal is dead. Note that the amplitude of the vibration in the epithelium is very subtle and ranges from 0.1 nm at minimum to 10 nm at maximum (Fig. 2<\/mark>); the difference is 100-fold. Your hearing can sense a buzzing of a mosquito that flies 3 m away from you as well as accept a jet engine sound emitted form an aircraft nearby. This difference of 1,000,000-fold in sound pressure levels is highly compressed to 100-fold in the motion in the sensory epithelium. The large dynamic range results from the nonlinear response mentioned above and this profile is crucially involved in establishment of the sharp tuning of our hearing.<\/span><\/p>\n<\/div>\n\n\n\n

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Figure 2\u3000Vibration profile of sensory epithelium<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n

Sensory hair cells are classified into two groups, outer and inner hair cells. Outer hair cells isolated from the cochlea can change their shape in response to electrical stimuli. This motility is likely to crucially contribute to the nonlinear response in the sensory epithelium. Nevertheless, it has not yet been fully elucidated \u2018in vivo<\/em>\u2019 how the hair cells move and their motion are associated with vibrations in the supporting-cell layer and\/or basilar membrane. To address these issues, we are developing an advanced laser interferometer<\/strong> and a unique optical coherence tomography (OCT)<\/strong> together with engineers and investigating the mechanisms underlying the characteristic vibrations in the sensory epithelium. For details, see the page of \u2018Analytical Instruments<\/strong>\u2019. We have also begun to study the pathological relevance of disorder of the vibrations to hearing loss.<\/span><\/p>\n\n\n\n

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Overview: How Does The Cochlea
of the Inner Ear Work?<\/strong><\/a><\/div>\n<\/div>\n<\/div>\n\n\n\n
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\u3000Project \u2777\uff1a <\/strong>
Biological Battery in the Cochlea<\/strong>\u3000<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n
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INSTRUMENTS<\/a><\/p>\n","protected":false},"featured_media":0,"template":"","research-content_cat":[16],"class_list":["post-173","research-content","type-research-content","status-publish","hentry","research-content_cat-rc-main2-child"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/wp-json\/wp\/v2\/research-content\/173","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/wp-json\/wp\/v2\/research-content"}],"about":[{"href":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/wp-json\/wp\/v2\/types\/research-content"}],"wp:attachment":[{"href":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/wp-json\/wp\/v2\/media?parent=173"}],"wp:term":[{"taxonomy":"research-content_cat","embeddable":true,"href":"https:\/\/www.med.osaka-u.ac.jp\/pub\/pharma2\/english\/wp-json\/wp\/v2\/research-content_cat?post=173"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}