Cochlear electrophysiology
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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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Cochlear electrophysiology

Cochlear Electrophysiology

Zemlin pp. 489-494


Electrical potentials

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


Stimulus independent vs dependent

Stimulus Independent

EP

IP

Stimulus Dependent

SP

CM

AP

Stimulus Independent vs. Dependent


Three dc potentials

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


Cochlear electrophysiology

+100 mV

Reticular Lamina

-50 mV


Two ac potentials

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


Differential electrodes

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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