Inner Ear Physiology Flashcards
What type of receptors are hair cells?
mechanoreceptors
Which type of hair cells have a lateral cisternae?
type 2
it’s a specialization of the ER similar to the SER of muscle cells
Which type of hair cells get 90% of the afferent innervation coming out of the ear?
type 1
What type of hair cell shares its afferent fibers with many other hair cells?
type 2 (not much specificity)
Which type of hair cells gets direct innervation from both afferent and efferent fibers? How is the other type different?
type 2
type 1 cells get their efferent indirectly - they synapse onto the afferent fibers and not the cell body
What does it mean to say that inner ear transduction is direction?
it means that displacement in one direction will cause depolarization and in the other direction will cause hyperpolarization
In the cochlea, positive deflection (with depolarization) occurs when the basilar membrane moves toward the ____ while negative defletion is towards the _____
positive deflection = towards the scala vestibuli
negative deflection = towards the scala tympani
Related to the stereocilia themsevles, deflection toward the ___ steroecilia will cause depolarization? How?
towards the tallest stereocilia
there are tip links that connect the stereocilia together and are attached to mechanically gated channels
movement toward the tall stereocilia puts tension on the tip links, pulling the gated channels open, allowing K+ to rush intot he cell causing depolarization
What allows for adaptation in the inner ear?
there is a motor complex (with actin and myosin7a) that maintain the tip link tension at a proper set point
this means some channels are always open and some are closed, so you always have a mehanism by which you can generate hyperpolarization
What components of the vestibular system sense angular acceleration (head rotation) and what detects linear acceleration (gravity)
the semicircular canals detect angular
the otolith organs (utricle and saccule) detect linear
Besides balance, posture, and coordination of head and body movement, what is the vestibular system responsible for
fixating the visual image on the fovea regardless of movement
If the input from the visual system and vestibular system are in conflict, which system does the brain believe? What’s the main symptom of this?
it believes the vestibular
it cause nystagmus as the brain tries to move the eyes to be in agreement with the vestibular system
What are the two situations (normally) wher eyou dont’ have any output from the semicircular canal hair cells?
at rest and at CONSTANT motion - it cares about changes *accelerations)
Describe what happens to the hair cells and cupula when the head starts rotating, reaches constant velocity, and stops rotating
starts - hair cells move but fluid doesn’t yet - they get displaced away from the movement
constant - hair cells and lfuid moving at the same rate, no defleciton
stops - the hair cells stop but the fluid keeps going for a bit 0 this displaces the cilia in the direction of the movement
Semicircular canals work in pairs, specifically…
the horizontal together
left anterior with right posterior
right anterior with left posterior
WIth head movement, depolarization will occur in the ___ direction as the head rotation
same direction
moving head to the right will cause depolarization in the right horizontal semicircular canal and hyperpolarization in the left horizontal
If you nod your head, how many of the 6 circular canals are being affected?
4 - both anterior and both posterior
What exam maneuver do you use to determine which canal is involved in paroxysmal vertigo?
Which is usually affected?
dix hallpike
it’s usually posterior canals
How do the otoliths detect gravity?
they are calcium carbonate seeds that sit on top of the matrix above the hair cells and they can cause stereocilia deflection in response to gravity
How are the hair cells oriented in the utricle compared to the saccule?
in both the utricle and saccule ther eis an organizing line down the middle called the striola
in the utricle, the tallest stereocilia are oriented towards the striola wihe in the saccule they are oriented away from the striola
this means you end up with depolarizaiton and hyperpolarizaiton in opposite directions between the utricle and saccule
a pure tone looks like what graphically?
a sine wave
frequency determines… and depends on…
intensity determiens…. and depends on….
frequency determines pitch and depends on wavelength
intensity determines loudness and depends on amplitude
What is intensity measured in?
decibels - remember it’s a log scale!
What part of the ear really determines what we hear? Why?
the middle ear - it reflects about 99.9% of the energy and the inner ear will really conduct exactly what it’s given, so the middle ear is the limiting factor
What are the three mechanisms of impedence matching in the middle ear?
- the TM is much bigger than the oval window - area ratio
- the handle of hte malleus is much bigger than the handle of the incus (level ratio)
- the TM is anchored around the outside so it will buckle more in the middle such that the force is concentrated there
Alterations int he impedance matching will result in a deficit of conductive or neurosensory hearing>
conductive
What are the two things that affect acoustic impedance in the middle ear?
the middle ear is better or worse at minimizing loss depending on frequency
the two properties associated with this are mass and stiffness (elasticity)
Heavier things will responate at __ frequencies
Stiffer things will responate at ___ frequencies
lower
higher
What frequency hearing loss will a patient experience in otosclerosis?
the ossicles are haivng bone layed down, so they’re increasing in mass
this means they will resonate at lower frequencies and you’ll have high frequency hearing loss
What frequency hearing loss will you have in an otitis media? As the condition worsens?
Initially, water builds up in the space increasing stiffnes, meaning the ear will resonate at highe rfrequencies and you’ll have low frequency hearing loss
but as infection progresses, gunk gloms on to the ossicles icnreasing their mass, so then you also have high frequency hearing loss
At what range of frequencies do humans hear best?
500 Hx to 5 KHz
As you move away from the 500 Hz to 5 KHz range, threshold for activation…
goes up
Before we reach saturation for audition we reach the…
pain threshold
How do audiograms compare the threshold intensity required to detect any given frequency?
they set the normal at 0, so 0 is a good result
as it goes up, the results are worse- it means you need a higher intensity to hear the frequency
How does a newborn’s range differ from ours?
they have wider range because they don’t have any hearing loss whatsoever yet.
they can here from about 100 Hz to 20 Khz
they lose it pretty quick though
How is the basilar membrane arranged? What determines this?
tonotopicaly!
low pitch tones (low frequencies) are near the apical portion
higher tones (highe rfrequencies) are near the basal portion
this is determined by the traveling wave and how it travels thorugh the membrane
True or false, the cochlea will conduct the sound in the same way regardless of how it was conducted.
true
Why is air conduction better than bone conduction if the cochlea doesn’t care?
amplification delivered by the middle ear makes air conduciton better
Traveling waves will always start at the __ and travel towards the ___
start at the base and go twards the apex
higher frequencies reach their peak near the base and lower freuqnecies reach their peak near the apex
Why do the different regions of the cochlea resonate differently?
number of cells icnreases going towards the apex
stiffness will be greater at the base (resnate higher frequencies)
How are the outer hair cells involved in a positive feedback mechanism for hearing and otoacoustic emissions?
They use their receptor potential to exert force ont he basilar membrane by contracting, thus amplifying the force and sound
this force creates its own fluid wave which is conducted back thorugh the perilymph to vibrate the middle ear appratus and generate it’s own sound - the otoacoustic emissions
What affect does the outer hair cells’ contractility have on threshold levels?
they amplify the activity of the inner hair cells such that threshold level is lower - doesn’t take as much itnensity for activation
How can you utilize otoacoustic emissions (and the non-linearness of the auditory system) clinically?
you can use it to test hearing in infants since they can’t respond to questions
WHat produces the endolymph?
the stria vascularis
What is the endocochlear membrane potential and K+ concentration? What does this mean for driving force?
the endocochlear potential is +80 mV (compared to -30 mV on the inside of the hair cells)
the K+ concentration is much higher outside than inside (150 mM)
this means the driving force for K+ is into the cell (both chemically and electrically)
this is why K+ is the ion responsible for the depolarization of the hair cells, not Na+
What transporter in the stria is affected by loop diuretics? What’s the effect?
the Na/K/2Cl transporter
side effects of loop diuretics include hearing loss
