Cochlear Electrophysiology Flashcards
Scala media is filled with what kind of liquid? What is the voltage of the liquid?
Endolymph, +80 mV, lots of potassium
Scala vestibuli is filled with what kind of liquid? What is the voltage of the liquid?
Perilymph, ~0 mV, lots of sodium
Scala tympani is filled with what kind of liquid? What is the voltage of the liquid?
Perilymph, ~0 mV, lots of sodium
What is the resting voltage of the outer and inner hair cells?
Outer hair cells have a -60 to -70 mV electrical charge. Inner hair cells have a -40 mV electrical charge.
Why is it important to have a potential difference across scala media and hair cells?
The potential difference can generate electricity, which is needed to power the cochlea. The potential difference also creates a large voltage gradient (125-150 mV difference) which drives the potassium ions into the hair cells.
What is the source of the endocochlear potential? What types of cells help generate it?
The endocochlear potential is a resting, electric polarization of the endolymph in the scala media. The endolymph is positively charged relative to the perilymph in the scala vestibuli and tympani.
The marginal and intermediate cells help generate the cochlear potential. The marginal cells are associated with the ion channels and pumps. The intermediate cells contain melanin, which is necessary to produce the endocochlear potential.
Where are the ion channels on the stereocilia?
The mechanically gated ion channels are thought to be located near the tips of the stereocilia.
Stereocilia must be fast enough to do what?
Stereocilia need to move fast in order to reproduce high frequency signals. The fast motion is helped by side links moving stereocilia in unison.
What are the cochlear potentials? Which respond to stimuli?
There are resting and active potentials. Resting potentials include the endocochlear and intracellular potentials. The active potentials include the cochlear microphonic, summating potential, and the compound action potential. Action potentials result from a change in electrical current due to an acoustic stimulus.
Which potential mimics the stimulus fine structure? Is it more like AC or DC?
The cochlear microphonic is a stimulus related potential and mimics the stimulus. The potential represents the summation of response (receptor currents) from individual hair cells. It is more like an alternating current (AC) and is generated mostly by outer hair cells.
Which potential mimics the stimulus envelope? Is it more like AC or DC?
The summating potential is a step-like current, more like a direct current, that follows the stimulus envelope. The summating potential. The source of the summation potential is not clear, as it could come from mostly inner hair cells and some outer hair cells.
Where is the compound action potential generated?
The compound action potential originates in the spiral ganglia, which causes the response of the auditory nerve.
What goes up to higher frequencies, the cochlear microphonic or the inner hair cell potential?
The cochlear microphonic.
What cells produce OAEs?
Outer hair cells
