L32 Auditory System Flashcards by Grace Lepis

how is sound generated?

by mechanical vibrations that generate pressure waves in the medium they are traveling in (Air, water etc.)

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high pressure waves have a ____ number of molecules per volume

higher

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low pressure waves have a ____ number of molecules per volume

low

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define frequency, what are it’s units?

tone or pitch

measured in Hz (cycles per second)

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what is the range of frequency that the human ear can hear?

20-20,000 Hz

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define amplitude, what are it’s units?

intensity or loudness
measured in dB

normal breathing = 10 dB
jet engine = 150 dB

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what are the steps involved in sound production?

sound pressure waves enter EAM
produce vibrations on tympanic membrane
sound is amplified down the chain of ossicles (malleus, incus, stapes)
final ossicle vibrates the stapes which vibrates the oval window located in the cochlea
organ of corti in cochlea does signal transduction
hair cells transmit signal down CN8 which is the first element of the auditory pathway

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Because the tympanic membrane is ___ larger than the oval window, the force increases by ___because the area decreased by 20x (remember that F=P/A so if A↓, F↑)

20X

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what is the role of the chain of ossicles

act like a lever-arm which further amplifies the sound

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overall, how much does the middle ear amplify the pressure force

70-100x

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describe the Scala vestibuli and tympani - what are they filled with? what is the fluid composition similar to?

are continuous with each other
are filled with perilymph which has an
ionic composition that is similar to ECF

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describe the Scala media- what are they filled with? Why is there a high K+ concentration in endolymph in the scala media

filled with endolymph and is high

in K+ due to secretions from the Stria Vascularis

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what is the function of the basilar membrane

separates the Media from the

Tympani and supports the Organ of Corti

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what is contained within the organ or corti, what is that bathed in, why is this necessary

contains the hair cells which
are bathed in the endolymph compartment and
is necessary because of the high K+ concentration needed by the hair cells for signal transduction

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how do sound waves travel from the stapes to the cochlea

Movement of the stapes produces pressure on the oval window which moves the fluids within the cochlea

*This movement of fluids (not compression) is best described as traveling waves which are translated to the basilar membrane

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how do sound waves travel from the stapes to the cochlea

Movement of the stapes produces pressure on the oval window which moves the fluids within the cochlea

*This movement of fluids (not compression) is best described as traveling waves which are translated to the basilar membrane

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the basilar membrane acts as a _____ for sound frequencies. explain

“Place Code”

the amount of deflection of the basilar membrane is based on its mechanical properties at that particular point in the membrane

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the basilar membrane acts as a _____ for sound frequencies. explain

“Place Code”

the amount of deflection of the basilar membrane is based on its mechanical properties at that particular point in the membrane

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describe the base (close to oval window) of the basilar membrane? - describe, what type of frequency does it respond to?

narrow and stiff

HIGH frequencies

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describe the apex (near the helicotrema) of the basilar membrane - describe, what type of frequency does it response to?

wide and floppy

LOW frequencies

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define the envelope of waves?

the sum of the deflection of the basilar membrane at different stages of the travel of the wave

which as we now know exhibits variations from base to apex

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what are inner hair cells responsible for

signal transduction

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What do traveling waves on the basilar membrane cause a deflection of?

cilia on the hair cells that are attached to the basilar membrane

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what is the role of the outer hair cells?

amplifying the deflection of the basilar

membrane and therefore amplifying the output signal

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The outer hair cells have _____that cause them to _____ in the event of a depolarization

motor proteins | shorten

what happens if the shortening across many outer hair cells takes place in proper sync?

they can help push and pull the basilar membrane such that its deflection is maximized thus amplifying the outgoing signal.

what Brodmann's area is associated with the primary auditory cortex A1? what part of the cortex does that make up?

Broadmann Area 41 and 42 comprise the transverse temporal gyri

how is the primary auditory cortex organized - explain organization related to frequency and columns

topographical organization of A1 = tonotopic organized by frequency sensitivity along the rostro-caudal axis organized in columns that are grouped according to their pattern of input

what are the EE columns?

those that are Excited by both ears

what are the EI columns?

those that are Excited by ONE ear and Inhibited by the OTHER ear

where does the primary auditory cortex receive input from the thalamus?

in layer-4 where the thalamo-cortical fibers synapse *identical to the other primary sensory cortex area

what is Low Frequency Sound based on? Explain

time pressure waves from space will reach each ear at different times which is interpreted and understood to come from the given location

how is the time delay in low frequency sound detected? what is the name of the mechanism

by the binaural pathways to the superior olive (MSO) | by a mechanism known as Coincidence Detection

low frequency: what happens If the EPSP’s from each ear arrive at the superior olive at the SAME TIME (coincidence)

there will be a large signal

low frequency: what happens if the EPSP’s from each ear arrive at the superior olive at DIFFERENT TIMES (no coincidence)

there will be a smaller signal

what 2 things gives the understanding of where the sound is coming from?

The timing of EPSP arrival | signal size

what is high frequency sound based on Based on?

AMPLITUDE/INTENSITY

The amplitude varies based on the ____ created by the head if the source is____ to the midline

sound shadow | lateral

The amplitude received by one ear is _____ by the head causing a lower ___ and a lower ____versus the other ear who receives a signal without any dampening thus a higher signal

“dampened” amplitude signal

Fibers from one ear synapse?

in the ipsilateral superior olive as well as collaterals to the Trapezoid nucleus

what does the ipsilateral superior olive sends the output info to?

the cortex

where does the Trapezoid nucleus sends inhibitory fibers to?

the contralateral superior olive

the superior olive on each side has direct excitation _____and indirect inhibition from the ____side

ipsilateral | contralateral

what does the sum of the inputs at the superior olives result in?

contralateral inhibition and ipsilateral excitation

What happens If one side starts off with an intrinsically higher intensity?

its inhibitory contralateral will | hyperpolarize the opposite superior olive

Where is the localization and mechanism of LOW FREQ

in the medial part of the superior olive, using coincidence detection

Where is the localization and mechanism of HIGH FREQ

in the lateral part of the superior olive, using interaural amplitude differences

describe weber's test

Place the tuning fork on the forehead and see where the sound is louder, right or left? Normally, the person should say it is equal

using weber's test, how could you diagnose a conductive problem?

sound lateralized to the AFFECTED side (ipsilateral)

using weber's test, how could you diagnose a sensorineural problem

sound lateralized to the UNAFFECTED side (contralateral)

describe Rinne's test

after we know which side has a problem, the Rinne’s test will tell us what kind of problem we have The tuning fork is placed on the mastoid process and held there until the patient no longer hears the sound as it travels thru bone Once the patient states they no longer hear it (via bone), the fork is held in the air next to the ear Normal→ the air conduction should last longer and is louder due to amplification mechanisms utilized in air conduction

how can you diagnose conductive hearing loss using Rinne's test?

diminished air conduction; thus bone conduction is better and we now know that this is a problem with the conductive system and not the neurologic system

what is otosklerosis?

Fusion of the bony labyrinth (stapes to oval window) causing Conductive hearing loss of up to 40dB

what is vestibular schwannoma?

Tumor of Schwann cells in vestibular division of CN-8 causing Sensorineural hearing loss

what happens as a result of loss of hair cells?

Can also cause Sensorineural hearing loss May be due to aging or the exposure to high frequencies (+100dB) This loss cannot be replaced by cell division

describe cochlear implants

Consists of a microphone, electronic processor and many stimulating electrodes in the cochlea to help restore hearing The apparatus delivers sound directly to the cochlear nerve in the event that the hair cells are damaged/lost

define conductive hearing loss

hearing loss association with interference of sound transmission in the outer or middle ear

define sensorineural hearing loss?

hearing loss associated with pathology of the cochlea or the auditory n.

how is sound characterized?

1. frequency - tone/pitch 2. intensity - amplitude 3. point of origin

what are the 2 mechanisms of pressure amplification in the middle ear?

size difference | lever ratio of the ossicular chain

what is the first step in the sound transduction process

deflection of hair cell stereocilia

what is the second step in the sound transduction process?

opening of ion channels

what are the elements of the auditory pathway?

cerebral cortex - transverse temporal gyrus thalamus - medial geniculate nucleus midbrain - inferior colliculus pons - lateral lemniscus nucleus, superior olive, trapezoid nucleus medulla - cochlear nuclei auditory n. (CN 8) - spiral ganglion

define conductive hearing loss

hearing loss association with interference of sound transmission in the outer or middle ear

define sensorineural hearing loss?

hearing loss associated with pathology of the cochlea or the auditory n.

how is sound characterized?

1. frequency - tone/pitch 2. intensity - amplitude 3. point of origin

what are the 2 mechanisms of pressure amplification in the middle ear?

size difference | lever ratio of the ossicular chain

what is the first step in the sound transduction process

deflection of hair cell stereocilia

what is the second step in the sound transduction process?

opening of ion channels

what are the elements of the auditory pathway?

what is localization of low frequency sound based on?

interaural time difference

what is the localization fo high frequency sound based on

amplitude difference