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MH - Neur 3206 - Lecture 9 Handout.pptx

MH - Neur 3206 - Lecture 9 Handout.pptx - Hearing Sound...

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Hearing – Sound waves to sensory transduction
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Announcements Midterm is next Thursday (October 19) Covers Lectures 1 to 10 and Reading 1 Review class on Tuesday (Oct 17) worth your while to attend Today’s text: Chapter 11, First half
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What are we going to do today? What is sound? Structures and functions of the outer and middle ear Getting the sound waves to sensory neurons: the inner ear (Cochlea) Sensory transduction in inner hair cells Amplitude and frequency coding in the cochlea
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What is Sound? Sounds are created when objects vibrate Vibrations of an object cause molecules in the object’s surrounding medium (e.g. - atmosphere) to vibrate as well Sound waves: audible, sinusoidal changes in air pressure due to vibrating objects compressing and rarefying the air molecules Sound waves travel at a constant speed. Depends on medium Air = 340 m/s, Water = 1500 m/s Fig. 11.1
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Physical qualities of sound waves Frequency : For sound, the number of times that a pattern of pressure repeats per unit of time or distance (per sec, Hz) Pitch : Low frequency = low notes, High frequency = high sounds Amplitude : The magnitude of displacement of a sound pressure wave (dB, logarithmic scale) Loudness : perceived intensity or magnitude Illustration: http://www.slate.com/blogs/bad_astronomy/2014/11/14/cymatics_science_v_music.html Fig. 11.2
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Capabilities of human hearing Audible sounds range in frequency from 20 Hz to 20,000 Hz Ratio between faintest and loudest sounds is more than 1:1,000,000 (6 dB = doubling in magnitude of pressure)
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Where are we now? What is sound? Structures and functions of the outer and middle ear Getting the sound waves to sensory neurons: the inner ear (Cochlea) Sensory transduction in inner hair cells Amplitude and frequency coding in the cochlea
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Structures of the auditory system Fig. 11.3
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Structures of the outer ear Sounds are first collected from the environment by the pinnae Sound waves are funneled by the pinnae into the ear canal The length (~ 25 mm) and shape of the human ear canal enhances certain sound frequencies (2 to 6 kHz) The main purpose of the ear canal is to insulate the structure at its end—the tympanic membrane (eardrum)
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Structures of the middle ear Tympanic membrane is a thin sheet of tissue that forms border between the outer and middle ear Middle ear consists of three tiny bones (malleus incus stapes), ossicles, that transmit and amplify sounds to oval window of inner ear Ossicles are smallest bones in human body What do you observe about the physical size and connections of structures in the middle ear? Fig. 11.5
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Functions of the ossicles 1. Transmit sounds 2. Amplify sounds (why and how?) Why - needed to overcome extra resistance in transmission of sound waves from air to fluid-filled inner ear How? (P = F/SA) i) Joints between bones hinged so bones work like levers modest amount of energy on one side of fulcrum (joint) becomes larger on other (increases Force)
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