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Organization and Neuroanatomy.docx

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Paul Faure

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October 23 , 2013 Psych 3A03: Audition Organization and Neuroanatomy Cochlear Microphonic (CM) - CM is a stimulus driven AC potential - Amplitude of CM increases with stimulus and has wide dynamic range, but CM does saturate - Level increases in proportion to basilar membrane motion - Phase difference: travelling wave has to travel from base to apex and depending on the frequencies – high frequencies only occurring at the basal turn not the third turn (apex) - Frequency of oscillation of CM mirror stimulus - CM has been used to measure space-time pattern of basilar membrane displacement (i.e. the cochlear traveling wave) - CM can measure the traveling wave of the basilar membrane - Source of CM near boundary of scala tympani and scala media – thought to be the movement of OHC stereocilia Compound Action Potential (CAP) - Huge deviations at the beginning - CAP is stimulus driven AC potential - Not a true cochlear potential (but is recorded with cochlear electrodes) – due to the synchrony of all the nerve fibres exiting the cochlea - CAP is sum of individual action potentials from nerve fibres responding simultaneously - It is a whole nerve compound action potential - CAP latency varies as function of stimulus frequency due to travel time of basilar membrane traveling wave of displacement (delay = 2.5 to 4.0 ms) – high frequencies have shortest latencies and low frequencies have longest latencies and it takes time for the wave to travel up the cochlea Breakdown of Gross Cochlear Potentials 1. Gross cochlear response made up of sub-components corresponding to various anatomical structures (can be separates and identified with filters)  Signal ran through low pass filter gives DC potential  High pass filter left with AC potential 2. Compound action potential (CAP) is the result of synchronous activity of individual auditory nerve fibres 3. Summating potential (SP) reflects direct current (DC) component, mainly from inner haircells (IHCs) 4. Cochlear Microphonic (CM) closely resembles sound stimulus and reflects alternating current (AC) components, which mainly originate from outer haircells (OHCs) Haircell Receptor Potential (Intracellular) - Electrode inside inner haircells, outer haircells or inner haircell neurons - Recording shift in receptor potential of the haircells - The electrical response of haircells to an acoustic stimulus (receptor potential) has 2 components: a direct current (DC) t
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