10 -- Auditory system 1

10 -- Auditory system 1 - Auditory Neurophysiology Overview...

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Auditory Neurophysiology
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Overview of Structures Anatomy of the Ear
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Auditory Components Anatomy of the Ear
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Closer Look at the Cochlea Cochlea is a tubular structure that is coiled up in a spiral fashion, like a snail shell There are 3 separate chambers inside this coil Space inside tubes filled with fluid, not air like external and middle ear
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Closer Look at the Cochlea Cross-section of the cochlea 3 separate chambers easier to discern Part of cochlea that will transduce sound to neural signal found in scala media Called ORGAN OF CORTI ORGAN OF CORTI (yellow below)
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Closer Look at the Cochlea 2 chambers filled with PERILYMPH S. vestibuli S. tympani 1 chamber filled with ENDOLYMPH ENDOLYMPH S. media
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Closer Look at the Cochlea 2 chambers filled with PERILYMPH high Na+ / Low K+ S. vestibuli S. tympani 1 chamber filled with ENDOLYMPH ENDOLYMPH high K+ / Low Na+ high K+ / Low Na+ S. media If you measure the overall electrical charge of the endolymph compared to perilymph, it will be about 80mV more positive ENDOCOCHLEAR POTENTIAL ENDOCOCHLEAR POTENTIAL
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Physics of Sound Sound is a wave phenomenon Alternating compression/rarefaction of air
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Physics of Sound 2 properties of the waves to note: FREQUENCY expressed as waves/second (Hz) AMPLITUDE expressed in logarithmic scale (dB) Pitch (high/low) VOLUME VOLUME (loud/soft)
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Human Frequency Sensitivity 20Hz – 20,000Hz (20kHz) Common Volumes jet plane with afterburner 150 dB pneumatic hammer 120 dB loud radio 80 dB normal conversation 65 dB whisper 30 dB limit of audible noise 10 dB “Sportscenter” at night when wife 0.001 dB trying to sleep (but can hear TV anyway!!) Physics of Sound Several million fold difference in sound energy intensity!!!
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Transformation and Amplification of Sound Sound waves hit tympanic membrane Vibrates at same resonance as sound waves Tympanic membrane vibrations cause auditory ossicles to move – b/c they act as levers, movement motion amplified Interesting Trivia: ossicles are smallest bones in the body End Result = footplate of stapes pushes against oval window of cochlea Transformation of air waves into mechanical energy
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Transformation and Amplification of Sound Attenuation Reflex automatic control of ossicles to limit excessive movement
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Transformation of Sound Waves Movement of footplate against oval window sets up waves in perilymph of s. vestibuli transformed air waves into fluid waves Waves transmitted into s. media where transduction apparatus resides WEB ANIMATION Scala Vestibuli Scala Media Scala Tympani
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Transformation of Sound Waves Membranes separating s. media from other passages are flexible Fluid movements in perilymph translated into movement of BASILAR MEMBRANE BASILAR MEMBRANE This is the membrane upon which the organ of corti sits ANIMATION OF FLUID MOVING BASILAR MEMBRANE AND ORGAN OF CORTI
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10 -- Auditory system 1 - Auditory Neurophysiology Overview...

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