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20 Cards in this Set
- Front
- Back
What type of receptor is a hair cell
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mechanoreceptor
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What type of stimulus do auditory and vestibular hair receptors detect?
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auditory: pressure waves (no such thing as a sound wave)
vestibular: fluid motion |
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why are they called stereocilia
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difference in hair cell length provides directionality
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stereocilia TOWARDS kinocilium
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If the stereocilia are depressed toward the kinocilium, this will open cation channels. Entry of potassium from the endolymph will depolarize the cell. This depolarization leads to an opening of calcium channels with an influx of calcium into the cell. This releases a neurotransmitter, which may be glutamate, which is stimulatory to the afferent nerve just below the hair cell. Thus initiating action potentials that carry the information to the central nervous system
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stereocilia away from kinocilium
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If the stereo cilia bend away from the kinocilium, the cell is hyperpolarized and no neurotransmitter is released.
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perilymph composition is most similar to what
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CSF
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is endolymph similar or dissimilar to perilymph
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dissimilar; high K conc produced by stria vascularis (lsk)
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endolymph production and composition
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Endolymph is high in potassium and has a +80 mV potential difference from perilymph in the cochlea and approximately 140 mV difference across the hair cell membrane ( this difference is essential for proper hearing).
high potassium, low sodium |
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perilymph production and composition
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Produced by fibrocytes that line the scala vestibuli and the scala tympani (analogous to CSF with low potassium and high sodium)
The Cochlear and vestibular chambers of perilymph communicate with each other through a small opening called the helicotrema low potassium, high sodium |
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What is the function of the large potential difference between the endolymph and hair cell membrane
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high sensitivity to sound
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Pitch
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= Frequency
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Loudness
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Amplitude of wave; spatial summation and outer hair cell stimulation indicates to CNS that sound is louder
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What happens to hearing w age?
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Loss of sensation of sound on either end of the spectrum
Decreased sensitivity so soft sounds are not heard as well Lack of discrimination of sounds so the elderly hear well when talking one on one but do not hear well in crowds |
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A pressure wave moves the stapes as mentioned earlier and this wave is transmitted to the inner ear at the oval window
This wave influences the pressure in the various chambers and based on frequency it will induce movement in the basilar membrane at a point corresponding to the frequency of the wave High frequencies close to the oval window and lower frequencies farther away |
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medial superior olivary nuclei
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medial nuclei detects direction by the time lag between acoustic signals entering the ears
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Conduction deafness
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impairment of tympanic membrane or ossicles
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Nerve deafness
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impairment of the cochlea or the auditory nerve
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are the semicircular canals filled with perilymph or endolymph
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endolymph (high K, low Na)
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The cells in the direction of the turn fire faster and the cells opposite the turn are inhibited
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This slide indicates the level of discharge in terms of action potentials that would be fired from one side of the vestibular apparatus. Notice, there is a tonic level of discharge before motion begins and the hair cells are not being bent in either direction. Notice at the initiation of motion, there is a rapid increase in the number of action potentials that are fired as the hair cells are being bent toward the kinocilium. As the rotation continues and the fluid begins to move, the hair cells will no longer be bent as much toward the kinocilium and will become more upright again and you see that the discharge returns back down toward that tonic level. Once the motion of the fluid becomes constant we are back to the tonic discharge rate. Now when we stop rotation, the opposite occurs and the fluid is still moving while the head has stopped moving. This will move the stereocilia away from the kinocilium and you see a decrease in the number of action potentials being fired until that fluid begins to slow down and as it comes closer to a stop, notice that the number of action potentials being fired starts to return back up to the tonic level. This is how the brain can interpret whether you are moving and by summing the effects in each of these various tubules the brain can interpret the direction of motion as well.
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