Week 6.3 Flashcards
Where are the CN VIII cell bodies located?
- vestibular (aka Scarpa’s) ganglion
- auditory ganglion
Where are the CN VIII cell bodies located?
- vestibular (aka Scarpa’s) ganglion
- auditory ganglion
CN VIII afferents synapse in which nuclei?
vestibular and cochlear
Normally, the only fluid filled part of the ear is what?
the inner ear
What causes depolarization of auditory hair cells?
movement of the stereocilia in the direction of the kinocilium
What are otoliths?
calcium carbonate crystals embedded in a glycoprotein matrix atop vestibular hair cell sin the macular organs, which shift with gravity and bend stereocilia
What is the crista ampullaris?
a ridge of tissue in the semicircular canals in which vestibular hair cells are embedded
What is the cupula?
a tall glycoprotein matrix mass above the crista-ampullaris into which vestibular hair cells for the kinetic labyrinth are embedded
Fluid flowing through the semicircular canals deflects what?
the cupula
The Romberg test is a ____ test.
sensory
Performing normally on the Romberg test requires two of what three systems to be functional?
- visual
- proprioception
- vestibular
Describe the pathway for sound into the inner ear.
- external auditory meatus
- tympanic membrane
- meatus
- incus
- stapes
- oval window
Name three functions of the middle ear.
- impedence matching
- pressure equalization
- gain control of vibrations reaching the inner ear
CN VIII afferents synapse in which nuclei?
vestibular and cochlear
Normally, the only fluid filled part of the ear is what?
the inner ear
What causes depolarization of auditory hair cells?
movement of the stereocilia in the direction of the kinocilium
What are otoliths?
calcium carbonate crystals embedded in a glycoprotein matrix atop vestibular hair cell sin the macular organs, which shift with gravity and bend stereocilia
What is the crista ampullaris?
a ridge of tissue in the semicircular canals in which vestibular hair cells are embedded
What is the cupula?
a tall glycoprotein matrix mass above the crista-ampullaris into which vestibular hair cells for the kinetic labyrinth are embedded
Fluid flowing through the semicircular canals deflects what?
the cupula
The Romberg test is a ____ test.
sensory
Performing normally on the Romberg test requires two of what three systems to be functional?
- visual
- proprioception
- vestibular
Describe the pathway for sound into the inner ear.
- external auditory meatus
- tympanic membrane
- meatus
- incus
- stapes
- oval window
Name three functions of the middle ear.
- impedence matching
- pressure equalization
- gain control of vibrations reaching the inner ear
What is impedence matching?
preventing the loss of pressure at the oval window as sound goes from air to fluid conduction
The Eustachian tube connects what?
the middle ear with the nasopharynx
What muscles can change the stiffness of the tympanic membrane and dampen movement of the stapes?
- tensor tympani
- stapedius
What mechanism within the middle ear protects cochlear hair cells from loud sounds?
the tensor tympani and stapedius
The membranous labyrinth divides the bony labyrinth of the cochlea into what layers?
- scala vestibuli
- scala media
- scala tympani
The stapes transmits sound waves into which region within the membranous labyrinth of the cochlea?
the scala vestibuli
Auditory hair cells sit on what structure?
the basilar membrane
There are how many rows of inner and outer hair cells?
one row of inner and three of outer
What area within the membranous labyrinth of the cochlea is filled with endolymph?
the scala media
What is the stria vascularis?
an outer portion fo the membranous labyrinth of the cochlea that pumps potassium ions into the scala media
What is the tectorial membrane?
a membrane that sits atop auditory hair cells to displace stereocilia when sound vibrations move the basilar membrane
Describe the passage of sound waves through the inner ear.
- oval window
- scala vestibuli (perilymph)
- vestibular membrane
- scala media (endolymph)
- basilar membrane
Describe how auditory hair cells become depolarized.
- the tectorial membrane scrapes against the stereocilia, displacing them
- if this occurs in the direction toward the kinocilium, it induces a potassium influx that depolarizes the cell
Describe the ionic composition of endolymph?
high in potassium
How is sound information organized in the auditory system?
according to frequency
How is tonotopic organization achieved within the cochlea?
the basilar membrane varies in width and stiffness throughout the cochlea such that different frequencies of sound stimulate specific parts of the basilar membrane and corresponding hair cells
Describe the width and flexibility of the basilar membrane at the base of the cochlea.
narrow and stiff
The base of the cochlea is more sensitive to what kinds of sounds?
high frequency sounds
Which population of hair cells are actually responsible for transducing sound waves?
inner hair cells
What is the function of outer hair cells?
modify basilar membrane movement to alter its stiffness and sharpen frequency tuning
What hair cell population is more susceptible to damage?
outer hair cells
What neurons innervate outer hair cells?
motor efferents from the superior olivary nucleus in the pons
At what point does the auditory pathway become bilateral?
above the level of the cochlear nucleus
Where is the auditory cortex?
on the lower bank of the lateral sulcus
Describe the pathway for auditory information.
- auditory ganglion cells
- cochlear nucleus
- inferior colliculus
- medial geniculate nucleus
- auditory cortex
What is the role of the superior olivary nucleus?
control outer hair cell activity
What are two ways you can test the hearing of babies?
- auditory brainstem response
- otoacoustic emissions
If an individual has no otoacoustic emissions, what is damaged?
outer hair cells
As we age, what frequency of sounds do we lose the ability to hear?
high frequency
Our threshold for hearing is lowest in what range of frequencies?
those used for speech
What is an audiogram?
a graph of thresholds for given frequencies, relative to the average at each frequency
What is conductive hearing loss?
impaired conduction of sound through the external or middle ear
What is sensorineural loss?
pathology of the inner ear or 8th nerve
The most common central hearing disorder is what?
an acoustic neuroma
Bone conduction tests what kind of hearing?
sensorineural
Describe the results of a Weber test.
- normal if sound doesn’t localize to one side
- conductive hearing loss if localizes to the affected ear
- sensorineural hearing loss if it localizes to the unaffected ear
In practice we say that normal hearing is in what range on an audiogram?
up to 20 dB HL
How does conductive hearing loss appear on an audiogram?
- air conduction will be low
- bone conduction will be normal
How does sensorineural hearing loss appear on an audiogram?
both air and bone conduction tests will be low
How does a mixed hearing loss appear on an audiogram?
- air conduction very low
- bone conduction somewhat low
What are three common causes of conductive hearing loss?
- impacted cerumen
- otitis media (middle ear infection)
- otosclerosis
What is otitis media?
a middle ear infection
What is otosclerosis?
an overgrowth of bone in the middle ear auricles causing them to become stiff, leading to conductive hearing loss
Name some common causes of sensorineural hearing loss.
- perinatal infection
- long-standing otitis media or otosclerosis
- hereditary
- high intensity sound
- ototoxic drugs
Name a commonly used ototoxic dug.
aspirin
High intensity sound will cause what kind of hearing loss?
sensorineural
While ___ hair cells are more susceptible to damage, damage to ___ hair cells causes a more profound hearing loss.
- outer more susceptible
- inner more significant
How can we treat sensorineural hearing loss?
- hearing aids
- cochlear implants
What is Meniere’s disease?
a disorder of hearing loss due to an excessive amount of endolymph in the cochlea
How is Meniere’s disease treated?
with a low salt diet and diuretics
What are the symptoms of Meniere’s disease?
- fluctuating hearing loss
- fluctuating rotational vertigo
- fluctuating tinnitis
What is tinnitus?
the perception of a phantom sound
Tinnitus most commonly accompanies what?
cochlear hair cell loss
What is the difference between objective and subjective tinnitus?
- objective is due to pulsation of a blood vessel
- subjective is due to dysfunction of the auditory system
