Physiology of Auditory and Vestibular systems Flashcards
Where in the basilar membrane do high and low frequency (pitch) sounds get maximum deflection?
High - Base near the oval and round windows (narrow and stiff)
Low - apex near the helicostrema (wide and flexible)
Describe the tonotopy concept
Each sound wave is deflected at some point in the basilar membrane, depending on its frequency
Define the following
Sound
Amplitude
Frequency
- air pressure oscillations
- intensity of sound pressures (measured via dBs)
- number of oscillations per second
Why is the vibration of the basilar membrane important?
Cochlea is a closed structure, so vibration of the basilar membrane will cause pressure change = force on tectorial membrane connected to the outer hair cell stereocilia tips = movement of stereocilia
What triggers the depolarization of hair cells?
Sterocilia moves > tip links connect them all > force on all the stereocilia > TRPA1 channels open
What type of channels are the TRPA1 channels? Why is this type important?
Mechanotransduction channels. Important because capable of rapid, immediate effects and very sensitive to stimuli since they don’t require receptor potentials
*What are the features of the endolymph?
Bathe the apical end of the hair cells
Rich in potassium, low in sodium (ICF like)
Found in scala media and made by the stria vascularis
What are the features of the perilymph?
Bathe the basal end of the hair cells
Low potassium, high sodium (ECF like)
Found in scala vestibuli and tympani
Describe the depolarization of the stereocilia
K+ rich in endolymph > TRPA1 opens and lets all this K+ into the hair cell = depolarization > Ca2+ entry releases the Glu vesicles > released at synapse on the cochlear nerve afferents > AP sent to CNS
What does upward and downward basilar displacement result in hair cells?
Upward = lateral stereocilia displacement = depolarization Downward = hyperpolarization
Why are inner hair cells important for hearing?
Most cochlear nerve afferents are from the inner hair cells and these need to be depolarized to get any hearing. Outer hair cells are amplifiers
Why is the stria vascularis important?
Has processes that wrap around the capillaries of a plexus. K+ is released from the capillaries into the endolymph and bathes the stereocilia. The presence of lots of K+ in the endolymph thanks to stria vascularis helps with depolarization (reaching the threshold positive potential of +80 mV)
What is the importance of the endocochlear potential?
+80 mV. Pretty positive and maintained by stria vascularis by letting the K+ from capillaries enter to reach depolarization threshold.
What happens when stria vascularis is compromised?
Endocochlear potential is lowered and there is less depolarization of the hair cells = hearing loss
What are the features of the inner hair cells?
Source of the auditory info
Arranged in single layer
Synapse at primary afferents at spiral ganglion
What are the features of the outer hair cells?
Amplifies sound info
Arranged in 3 rows
Synapse at primary afferents at spiral ganglion
What are otoacoustic emissions?
Retrograde movement of the outer hair cells (from inner ear to TM) = ear itself produces sound
Anatomical basis of the otoacoustic emissions
OAEs originate from the superior olive efferents (olivocochlear efferents). Medial olive neurons stimulate the outer hair cells while lateral olive neurons innervate inner hair cells.
How are OAEs used for testing?
What can it and cannot test?
- OAEs are generated in response to sound stimuli, so give patient sound stimuli and read the low intensity OAEs that come back as a response.
- It can test sensorineural hearing loss but not auditory neuropathy
What is the role of olivocochlear efferents in protecting the cochlea?
Prevents too much physical stimulation of the basilar membrane by controlling movement of inner and outer cell movements
What is the role of middle ear efferents in protecting the cochlea?
Attenuates sound to avoid damage from TM to stapes (via contractions of tensor tympani (CN V) and stapedius (CN VII))
Damage to middle efferents = tinnitus
What is the role of autonomic efferents in protecting the cochlea?
Regulates tone (constriction) of cochlear blood supply (via CN VIII)
*Role of DCN vs role of VCN in auditory processing
DCN = sound + somatosensory integration VCN = begins processing sound features
*Role of MSO vs LSO in auditory processing
Both receive glutamate input
MSO - time differences to localize sound
LSO - intensity differences to localize sound
*Role of inferior colliculus in auditory processing
Suppresses info related to echoes since this interferes with localization
Time and intensity differences localize into IC to help localize origin of sound
*Role of MGN in auditory processing
Info from features of sound converge here > processes features of sound > send to primary auditory cortex
*Role of Primary auditory cortex in auditory processing
Conscious perception, higher order processing of sound
*Role of secondary auditory association cortex in auditory processing
More complex sounds (music), identifying sound and speech
How does a cochlear implant do and how does it work?
Help with sensorineural hearing loss due to hair cell or cochlear nerve damage.
Has a receiver and electrode array. EA is in the cochlea by the CN VIII afferents and stimulates a nerve fiber on the basilar membrane
What types of movement do these detect? Anterior semicircular canal Horizontal semicircular canal Posterior semicircular canal Utricle Saccule
- falling forward
- rotating around
- falling backward
- moving forward and backward
- moving up and down
