ASLP 334 Cochlear Electrophysiology Zemlin pp

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 334 Stimulus 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 mV Reticular Lamina +100 mV

Lecture 7 ASLP 334 Two AC Potentials Cochlear Microphonic (CM) Reproduces frequency and waveform of a sinusoid perfectly Fig (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 Bék é sy’s Traveling Wave Theory