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