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Cochlear Electrophysiology

Cochlear Electrophysiology. Zemlin pp. 489-494. Electrical Potentials. DC vs. AC Direct Current = stimulus doesn’t change with time, constant; i.e. battery Alternating Current = always changing over time, looks like a sine wave Stimulus Dependent vs. Stimulus Independent

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Cochlear Electrophysiology

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  1. Cochlear Electrophysiology Zemlin pp. 489-494

  2. Electrical Potentials • DC vs. AC • Direct Current = stimulus doesn’t change with time, constant; i.e. battery • Alternating Current = always changing over time, looks like a sine wave • Stimulus Dependent vs. Stimulus Independent • Stimulus Dependent = potentials only present if there is an acoustical sound present • Stimulus Independent = potentials always present with and without acoustical stimuli

  3. Stimulus Independent EP IP Stimulus Dependent SP CM AP Stimulus Independent vs. Dependent

  4. Three DC Potentials • Endocochlear Potential (EP) • Békésy discovered EP by putting the electrode in the scala media and discovered a +100 mV potential with respect to a neutral point on the body • Tasaki discovered EP was due to the Stria Vascularis • Intracellular Potential (IP) or organ of corti potential • Recorded -50 mV inside cells of organ of corti • Summating Potential (SP) • DC that is only during very loud intensities of acoustic stimulation

  5. +100 mV Reticular Lamina -50 mV

  6. Two AC Potentials • Cochlear Microphonic (CM) • Reproduces frequency and waveform of a sinusoid perfectly • Fig. 6-115 (p. 492) • Generated from OHC • Action Potential (AP) • Electrical activity from the VIII Nerve • Can be measured from anywhere in the cochlea or in the auditory nerve

  7. Differential Electrodes • Measure the CM, we also measure the AP unless we use differential electrodes • Tasaki (1954) was able to separate the CM & AP by using differential pair of electrodes • One electrode above reticular lamina (Scala Media or Scala Vestibuli) and the other electrode in the Scala Tympani • By changing the polarity, the AP cancels out, while the CM is doubled in amplitude • This proved Békésy’s Traveling Wave Theory

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