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Afferent and Efferent Physiology.docx
Afferent and Efferent Physiology.docx

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McMaster University
Paul Faure

October 22 , 2013 PSYCH 3A03: Audition Afferent and Efferent Physiology Inner Haircell Connection to CNS - IHC synaptically connected to all type I spiral ganglion neurons forming a radial afferent system going to cochlear nucleus - Lateral efferent system arises from small neurons in ipsilateral lateral superior olivary (LSO) complex and brings feedback control to the IHC/type I afferent synapse Outer Haircell Connection to CNS - OHC synaptically connected to a few small endings of type II spiral ganglion neurons forming the spiral afferent system going to cochlear nucleus - Medial efferent system arises form large neurons from the both the ipsilateral and contralateral medial superior olivary (MSO )complex Radial versus Spiral Nerve Fibers - Type I (large, myelinated) spiral ganglion neurons have a single synaptic ending radially connected to IHC Electric Potentials - The motions and interactions of various cochlear structures generate electric potentials - Cochlear electric potentials tell us how the ear works - An electrical potential is potential energy per unit of charge associated with a static (time-invariant) electric field - An electric potential is established whenever there is a concentration difference in charged ions between 2 regions (e.g. across a cell membrane) - Electric potentials are present in all cells that regulate the ionic content of their cytoplasm with respect to the ionic content of the extracellular environment Cells have a Resting Electric Potential - Passive channels - Ion channels open or close when there is a potential Electrodes Measure Electric Potentials - Electrical potentials are measured with electrodes  Anything along which ions can flow  Wire electrodes (e.g. tungsten, silver)  Glass electrodes (e.g. borosilicate pulled to fine tip) - We use electrodes to measure the electric potential difference between 2 sites - Therefore 2 electrodes are necessary: 1. Recording electrode 2. Reference electrode - Recording electrode measures the electric potential difference at the site of its penetration relative to the site where the reference electrode is placed Measuring Electric Potentials - Inside of the axon is negatively charged - When the two electrode are no the outside there is a 0 potential difference - When one electrode is pushed in the cell membrane there is a negative potential with respect to the outside of the cell - DC potential (constant) - Around -70mV Resting Potential is Based on all Ions - Intracellular: more potassium, less sodium - Extracellular: more sodium than potassium - If a sodium channel opens, sodium flows down its chemical gradient into the cell to the point where the charge begins to oppose the charge gradient Measuring Electric Potentials - -70mV resting potential AC vs. DC Electric
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