Auditory Flashcards
what is tonotopy
decomposition of complex sounds into constituent tones/frequencies (acoustical decomposition) spatially along the length of the choclear basilar membrane
what does the eustachian tube connect
what does it help do
is it usually open or closed
the middle ear w/ the nasopharynx
- helps to equalize the pressure btwn the middle ear and throat (nasal cavity)
- usually closed but opens during swallowing
what does the pinna aka auricle do to sound waves
collects and funnels sound waves and directs them into the external auditory meatus (ear canal) which terminates at the tympanic membrane
what causes the tympanic membrane to vibrate
the sound waves (condensations and rarefactrions of air molec) push on the tympanic membrane, pushing it back and forth, causing it to vibarate
what is the tympanic membrane innervated by
CN10 (spinal nucleus of V) for sensation
-ex why ur ear hurts in earache
what is the function of the outer ear? middle ear? inner ear?
outer: function=to collect sound waves (air)
middle: function-impedance matching (air)
inner: function=sound transduction (fluid)
what is the tympanic membrane connected to
the 3 smallest bones in the body-the malleus, incus, stapes
when the tympanic membrane is set into motion by the sound wave, the vibrations are transmitted across the middle ear by what
the conductive system of bony ossicles
-the stapes foot plate then “kicks in the oval window” to deliver a pressure wave to the fluids of the cochlea
the middle ear improves the system by how many dB
30dB
- what happens in the inner ear
- where will the nerve impulses travel
- where sound is transduced through mechanical vibrations on hair cells to nerve impulses
- these nerve impulses travel in the first order neurons in the spiral ganglion, which will project via CN8 to the dorsal and ventral cochlear nuclei at the level of the highest medulla
which chamber is the stapes (at oval window) connected to? waht about the round window?
oval: upper chamber (SV)
round: lower chamber (ST)
where is the organ or corti located
scala media
- what is the fluid composition like in the upper, middle, and lower chambers
- why is this importatn?
-ST and ST are high in Na, low in K
SM is high in K and low in Na
-the basilar membrane separates SM from ST so it is in contact w/ both endolymph and perilymph and this creates one of the largest voltage gradients in the body
(endocochlear potential)
where does sound transduction take place
at the hair cells (mechanoreceptors)
how are the hair cells organized in the organ of corti
single row of inner hair cells
3 rows of outer hair cells
what are the 2 important membranes of the organ of corti
the basilar membrane beneath the hair cells and the tectorial membrane lying over the hair cells
wehre are high frequencies coded on the cochlea? what about low freq?
high freq: coded down at the base of the cochlea (part closewr to the stapes)
low: up at the apex of the cochlea (apex is closer to the helicotrema)
what is the bony core of the cochlea
sprial ganglion
-in the cochlea’s bony modiolus
what do the peripheral processes of the spiral ganglion innervate?
waht do the central prcosses leave as?
- peripheral procsesses innervate the hair cells (mainly IHC)
- central leave as the cochlear nerve (CN8) and the CN8 fibers head straight for the cochlear nuclei (dorsal and ventral) in the highest medulla)
where do the central processes of the bipolar cells of the spiral ganglion synapse at?
what do they make up?
where does CN8 travel inside?
synapse inside the brainstem
make up the auditory division of CN8
a small bony canal called the Internal auditory meatus (IAM)
after the cochlear nuclei, wehre do these secondary auditory fibers go?
f
where do the dorsal cochlear nucleus receive input from?
wehre do they project?
receives input from Cn8
projects contralaterally to lateral lemniscus
where do the ventral cochlear nucleus receive input from?
where do they project? how do they project?
- receives input from CN8
- projects to dorsal cochlear nucleus, which then projects contralaterally to later lemniscus
- projects bilaterally (ipsi and contra) to the sup olivary nuclei
what are the superior olivary nuclei important for
sound locatlizatoin
fibers from the ventral cochlear nucleus converge on the ______ of each side
superior olive
where does the lateral lemniscus receive input from
contralateral cochlear nuclei
superior olivary nuclei
the lateral lemniscuc is connected to the contralateral lemniscuc via….
commissural fibers
wehre does the lateral lemniscus project to
nucleus of the inf colliculus
where does the inf colliculus receive input from
lateral lemniscus (info from both ears)
- receives fibers directly from dorsal cochlear nucleus
- receives fibers from ventral cochlear nucleus via sup olivary nucleus
does a unilateral lesion at the inf colliculus give unilateral deafness?
no bc it receives input from both left and right ears
where does the inf colliculus project to
medial geniculate via the brachium of the inf colliculus
also projects to sup colliculus (so your head and eyes can react to an auditory stimulus)
whre do auditory radiations travel w/in
wehre will they synapse
post limb of the internal capsule (PLIC)
-they will synapse in the auditory cortex (Heschl’s gyrus) in the temporal lobe, right inside the lateral sulcus
- wehre do the descending coritcospinal tracts coming from the Betz cells of the motor cortex coalesce and travel in
- wehre do the corticobulbars coming from the motor cortex descend in?
PLIC
genu
after leaving PLIC, auditory radiations synapse in the
primary auditory cortex in the temporal lobe
wehre do you find heschl’s gyrus? (the primary auridotry cortex)
inside the lateral fissure, in the temporal lobe, on the superior aspect of it
why is there no use in lateralizing a lesion after the cochlear nucli
bc the auditory pathway is both crossed and uncrossed
at the superior olivary nuclei, you have the first binaural cells – cells that have responses in the left and right ears. You know they accept input from the two cochlear nuclei, ipsilateral and contralateral.
what is conductive hearing loss
if you lesion the outer or middle ear
- esp the middle ear which gives you 30dB loss
- common and treatable
what is sensorineural hearing loss
if you damage the areas of the cochlea (ex hair cells), CN8, CNS (central auditory pathway)
-incurable and permanent
what is presbycusis
loss of hair cells at the BASE of basilar membrane
-bilateral cause of irreversible hearing of high frequencies in the elderly (can still hear low)
what are some causes of unilateral sensorineural deafness
- cochlea of one side
- CN 8 (auditory division) of one side
- dorsal and ventral cochlear nuclei of one side
-damage rostral to the cochlear nucleus does not result in deafness, but may cause deficits of sound localization
what is an acoustic neuroma
aka vestibular schwannoma bc arises from vestibular division
it is a tumor arising from schwann cells of CN8, not from the nerve itself
- benign, slowly growing
- cause of unilateral sensorineural deafness
where is the origin of the GSPN
origin: sup salivatory nucleus
termination: lacrimal gland via sphenopalatine gang
fucntion: parasympathetic innervation to the lacrimal gland for tearing
course: para pre, synapses at sphenopal gang
where do the parasympatheitc postganglionics travel through to innervate
travel through the inf orbital fissure to innervate the lacrimal gland
what does the stapedius nerve terminate? what is its function
termination: stapedius muscle
function: dampen sound; lesion=hyperacusia
what are the 5 branches of facial expression
- GSPN
- stapedius nerve
- chorda tympani (motor and sensory component)
- motor to muscles of facial expression
- general sensory fibers
what do you get when a tumor affects CN 8? 7? 5? 6?
8: unilateral hearing loss
7: ipsi LMN facial paralysis
5: facial hypoesthesia (including lost corneal reflex)
6: ipsi abduction deficit
why is the middle ear able to do impedance matching (matches the impedance btwn the outer and inner ear)
in part bc the area of the tympanic membrane is many times larger than the area of the oval window
- like an “energy funnel” giving about 30dB gain
- minimize the reflections of sound waves and maximizes transfer
what will deliver the pressure wave to the fluids of the cochlea
stapes
what 2 muscles does the inner ear use to dmapen the transfer of sound?
what are the CNs that innervate them
what do they do?
- tensor tympani -innervated by CN5 (motor), tenses the tympanic membrane (reduce vibrations)
- stapes -innervated by CN7 (motor), limits movment of the stapes to dampen low freq sounds; lesion to CN7 here may result in hyperacusis
the choclea is coiled 2.5 times around its bony core called the …
where is the cochlea carved into
modiolus
-and the choclea is carved into the petrous portoin of the temporal bone
the cochlea consists of 3 fluid filled chambers
- what are the upper (scala vestibuili), middle (scala media), and lower (scala tympani) chambers called in labyrinth terms?
- what is each chamber filled w/
upper and lower are considered “bony labyrinth”
the middle is “membranous labyrinth”
upper and lower chambers are filled w/ perilymph
middle is filled w/ endolymph
where are SV and ST continuous w/ each other
at the helicotrema (a small opening at the apex of the cochlea)
-so when you push the stapes in, the round window bulges out
