aslp 334 cochlear electrophysiology zemlin pp. 489-494
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ASLP 334
Cochlear Electrophysiology
Zemlin pp. 489-494
Lecture 7
ASLP 334
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
Lecture 7
ASLP 334Stimulus Independent vs. Dependent
Stimulus Independent EP IP
Stimulus Dependent SP CM AP
Lecture 7
ASLP 334
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
Lecture 7
ASLP 334
-50 mV
Reticular Lamina
+100 mV
Lecture 7
ASLP 334
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
Lecture 7
ASLP 334
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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