BIOLOGY 2C03 Lecture Notes - Mechanotransduction, Sensorineural Hearing Loss, Ion

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Sound is a pressure wave, and pure tones can be characterized by amplitude (measured indirectly as db) and frequency. Dynamic range of hearing in humans is about 0-100 db (whisper to pain) and 20-20,000 hz. Chronic severely loud sound exposure kills hair cells. Ototoxic antibiotics, e. g. streptomycin or gentamicin, kills hair cells. Hearing loss of high frequencies with age, aka presbycusis: anatomy of the ear, outer ear, middle ear. Pinna: funnels and amplifies sound, sound shadows provide resolution of sound origin. External auditory canal: acts as resonant tube for 4 khz tones. Impedance matching of air to water sound transmission by two mechanisms (1) lever advantage of ossicles (malleus, incus, stapes) (2) oval window of stapes is smaller than eardrum. Middle ear muscles (tensor tympani, stapedius): restrict ossicle movement in response to loud sound to prevent damage. Damage in the middle ear is called conductive : inner ear (more on cochlea below)

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