speech 490 exam 2

1)The sound wave enters through the auricle, which funnels it through the EAC to the tympanic membrane.

2)The TM vibrates in accordance with the displacement of air molecules and therefore sets the ossicular chain (malleus, incus, and stapes) into motion.

3)The footplate of the stapes moves in and out of the oval window of the cochlea, displacing the fluids and creating what is called a traveling wave (TW).

-The TW is dependent on the vibratory inputs of the stapes.

-Cochlear fluids are non-compressible, so the partitions (scalae) will move or bulge in response to the fluid displacement, and the round window is responsible for absorbing or accommodating the energy created in the TW.

what is a simple way that sound enters the ear

In summary, the cochlea takes mechanical energy from the middle ear, converts it into chemical reactions, and ultimately turns it into electrical (nerve) impulses.

what is transduction

tonotopically

how is the cochlea organized

there is a point on the basilar membrane for each frequency where the hair cells respond best

what does it mean that the cochlea is tonotopically organized

this is the point of maximum displacement of cochlear fluid

when each hair cell on the basilar membrane responds best what happen

the tectorial membrane shears against the hair cells

after maximum displacement of the cochlear fluid what happens

the organ of corti

what rides on the basilar membrane

the sensory cells of hearing (OHC and ICH)

what does the organ of corti contain

stereocilia

each hair cell has tiny hairs on top called _________

tectorial membrane

where is the stereocilia of the outer hair cells embedded

they are not attached to the tectorial membrane but they are attached to each other with tip links

where is the stereocilia of the inner hair cells embedded

they open and close as they are moved by the tectorial membrane

what do the pores of the stereocilia do

filled with endolymph which is high in potassium ions

what is the scala media filled with

when the stereocilia are sheared towards the tallest stereocilia the potassium channels are opened. potassium from the endolymph rushes into the hair cell. also channels near the bottom of cell allow sodium ions to enter the hair cell

explain depolarization

change in charge causes the hair cell to release a neurotransmitter to the neighboring synapse of an auditory nerve fiber. the auditory neurons receive this neurotransmitter and fire an action potential

what does the change of charge cause for depolarization

when the stereocilia are sheared the other way, the excess potassium and sodium ions are pushed out of the ion channels. this is the inhibition of the process (no neurotransmitter is released)

explain hyperpolarization

when the hair cell depolarizes and then releases neurotransmitters, the neurotransmitters cause the nerves to fire

what is an electrical impulse

cochlear nerve, cochlear nucleus, superior olivary complex (SOC), lateral lemniscus, inferior colliculus, medial geniculate body, auditory cortex (heschl's gyrus & wernicke's area)

what is the central auditory pathway

cochlea coils around the modiolus and is tonotopically organized

explain the cochlear nerve

where the bundle of auditory nerve fibers are contained

what does the modiolus mean

outer nerve fibers code for higher frequency and the innermost nerve fibers code for the lowest frequency sounds

what does tonotopically organized mean

only receives input from one ear

what does each cochlear nucleus receive input from one ear or both ears

in the cochlear nucleus

what part does the auditory information get broken down and analyzed

where the auditory information really begins to get broken down and analyzed by ever splitting nerve fibers

what does the cochlear nucleus do

it is duplicated 3 times in the cochlear nucleus to create redundancy so there is more opportunities for the brain to understand

what happens to the tonotopic information from the cochlea in the cochlear nucleus

-receives information from both ears

- this is the first time the left ear crosses to the right and vice versa

explain the superior olivary complex (SOC)

-it is a pathway more than a structure

-largest tract of auditory nerves in brainstem

-nerve fibers are splitting so the bundle is large

explain the lateral lemniscus

located in the midbrain. the uppermost structure in the brainstem

explain the inferior colliculus

cochlear nucleus, superior olivary complex, lateral lemniscus, inferior colliculus

what structures are located in the brainstem

thalamus

where is the medial geniculate body located

information is sent to the auditory cortex

explain the medial geniculate body

within heschl's gyrus in the temporal lobe

where is the auditory cortex housed

auditory information is processed

explain the auditory cortex

language processing/comprehension occurs here (gives speech meaning)

what does wernicke's area do

a brief, all-or-nothing electrical pulse that travels up the neuron

what is an action potential

because either the neuron fires fully or it doesn't fire at all

why are action potentials all or nothing

auditory pathway

where do ABR measure patterns of action potentials

thousands of neurons fire together because their activity adds up and can be recorded on the scalp as the ABR waveforms. a single neurons action potential is too small to detect

does a single AP fire or multiple

represents a synchronized burst of neural firing at different points in the auditory system

what does each peak on an ABR represent

synchronous neural firing beginning at the auditory nerve up to the brainstem

what does an ABR represent

waves I-V

what waves do you focus on for an ABR

synchronized neural firing at different points along the auditory pathway

what does each wave of an ABR represent

auditory nerve function and brainstem integrity

what do ABR waves help is evaluate

objective since does not rely on patient

is an ABR objective or subjective

certain points contain large bundles of neurons firing together

what happens as nerve impulses travel up the auditory pathway

major firing areas

what is a neuro-generator site

located in brainstem, and continue up through the midbrain before projecting to the auditory cortex

where are most neuro-generator sites located

inferior colliculus

what is the highest structure an ABR goes to

wave I: portion of the auditory nerve closest to cochlea

wave II: portion of auditory nerve closest to brainstem

wave III: cochlear nucleus

wave IV: superior olivary complex

wave V: lateral lemniscus and inferior colliculus

what are the neuro-generator sites for waves I-V

neurodiagnostic and threshold

what are the two types of ABR testing

retrocochlear disorders

what do neurodiagnostic ABR look at

uses a loud click stimulus

results in more neural firing and gives better/best waveforms

looks at waves I,III,V

explain neurodiagnostic ABR

estimate thresholds for cases where traditional is too hard

what do threshold ABR look at

uses frequency specific stimulus called tone-bursts or chirps

lower stimulus level until can't see wave V

looks at one spot on the cochlea

explain threshold ABR

threshold

is threshold or neurodiagnostic ABR preferred for babies

neurodiagnostic

which ABR are latencies used for

absolute, interpeak, interaural

what are the types of latencies

what point in time

what does absolute latencies mean

wave I should occur at 1.5 ms

wave III should occur at 3.5 ms

wave V should occur at 5.5 ms

explain absolute latencies

wave I-III should be about 2 ms apart

wave III-V should be about 2 ms apart

wave I-V should be about 4 ms apart

explain interpeak latencies

the time in between waves

what does interpeak latencies mean

with normal hearing or symmetrical cochlear hearing loss, the latencies should not differ by more thna 0.30ms

normally unilateral

explain interaural latency differences

as you lower the presentation level, the waves will be smaller and latencies will not longer until they go away

explain latencies in threshold ABR

taxes the auditory system by increasing the rate (how many clicks per second is stimulus going) of the stimulation

what is a rate study

11.1, 17.1, or 19.1

what rate is used for a slow rate (record ABR before rate study)

51.1, 71.1, or 91.1

what rate is used for a fast rate

there will be an increase in latencies of there is a pathology

what will you see in the stimulus rate

to see if wave V increases significantly in latency or disappears all together

what are we looking at when we do a rate study

tone-bursts or chirps

threshold ABR uses frequency specific stimuli called

500, 1000, 2000, 4000 Hz

what are thresholds tested at

We are stimulating a more specific portion of the cochlea, so there won't be as much neural firing going on as with click stimulus, meaning we get smaller waveforms.

why do we only focus on wave V for threshold ABR

noise and artifact can look like a response when a response is not there.

why must waveforms be repeatable to be considered a response for threshold ABR

Once you believe you have found the patient's threshold, you need to go 5-10 dB lower to see if a response is given. Then repeat the intensity that you think is threshold to obtain a repeatable waveform.

what do you do when you think you found a patient's threshold for a threshold ABR

-500= -20

-1000= -15

-2000= -10

-4000= -5

what are the correction factors for a threshold ABR

dB nHL to dB eHL

when we use correction factors what are we changing the dB to