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20 Cards in this Set

  • Front
  • Back
What type of receptor is a hair cell
mechanoreceptor
What type of stimulus do auditory and vestibular hair receptors detect?
auditory: pressure waves (no such thing as a sound wave)

vestibular: fluid motion
why are they called stereocilia
difference in hair cell length provides directionality
stereocilia TOWARDS kinocilium
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
stereocilia away from kinocilium
If the stereo cilia bend away from the kinocilium, the cell is hyperpolarized and no neurotransmitter is released.
perilymph composition is most similar to what
CSF
is endolymph similar or dissimilar to perilymph
dissimilar; high K conc produced by stria vascularis (lsk)
endolymph production and composition
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
perilymph production and composition
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
What is the function of the large potential difference between the endolymph and hair cell membrane
high sensitivity to sound
Pitch
= Frequency
Loudness
Amplitude of wave; spatial summation and outer hair cell stimulation indicates to CNS that sound is louder
What happens to hearing w age?
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
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
medial superior olivary nuclei
medial nuclei detects direction by the time lag between acoustic signals entering the ears
Conduction deafness
impairment of tympanic membrane or ossicles
Nerve deafness
impairment of the cochlea or the auditory nerve
are the semicircular canals filled with perilymph or endolymph
endolymph (high K, low Na)
The cells in the direction of the turn fire faster and the cells opposite the turn are inhibited
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.