Inner Ear Physiology

Question 1

What type of receptors are hair cells?

Answer 1

mechanoreceptors

Question 2

Which type of hair cells have a lateral cisternae?

Answer 2

type 2

it’s a specialization of the ER similar to the SER of muscle cells

Question 3

Which type of hair cells get 90% of the afferent innervation coming out of the ear?

Answer 3

type 1

Question 4

What type of hair cell shares its afferent fibers with many other hair cells?

Answer 4

type 2 (not much specificity)

Question 5

Which type of hair cells gets direct innervation from both afferent and efferent fibers? How is the other type different?

Answer 5

type 2

type 1 cells get their efferent indirectly - they synapse onto the afferent fibers and not the cell body

Question 6

What does it mean to say that inner ear transduction is direction?

Answer 6

it means that displacement in one direction will cause depolarization and in the other direction will cause hyperpolarization

Question 7

In the cochlea, positive deflection (with depolarization) occurs when the basilar membrane moves toward the ____ while negative defletion is towards the _____

Answer 7

positive deflection = towards the scala vestibuli

negative deflection = towards the scala tympani

Question 8

Related to the stereocilia themsevles, deflection toward the ___ steroecilia will cause depolarization? How?

Answer 8

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

Question 9

What allows for adaptation in the inner ear?

Answer 9

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

Question 10

What components of the vestibular system sense angular acceleration (head rotation) and what detects linear acceleration (gravity)

Answer 10

the semicircular canals detect angular

the otolith organs (utricle and saccule) detect linear

Question 11

Besides balance, posture, and coordination of head and body movement, what is the vestibular system responsible for

Answer 11

fixating the visual image on the fovea regardless of movement

Question 12

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?

Answer 12

it believes the vestibular

it cause nystagmus as the brain tries to move the eyes to be in agreement with the vestibular system

Question 13

What are the two situations (normally) wher eyou dont’ have any output from the semicircular canal hair cells?

Answer 13

at rest and at CONSTANT motion - it cares about changes *accelerations)

Question 14

Describe what happens to the hair cells and cupula when the head starts rotating, reaches constant velocity, and stops rotating

Answer 14

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

Question 15

Semicircular canals work in pairs, specifically…

Answer 15

the horizontal together

left anterior with right posterior

right anterior with left posterior

Question 16

WIth head movement, depolarization will occur in the ___ direction as the head rotation

Answer 16

same direction

moving head to the right will cause depolarization in the right horizontal semicircular canal and hyperpolarization in the left horizontal

Question 17

If you nod your head, how many of the 6 circular canals are being affected?

Answer 17

4 - both anterior and both posterior

Question 18

What exam maneuver do you use to determine which canal is involved in paroxysmal vertigo?

Which is usually affected?

Answer 18

dix hallpike

it’s usually posterior canals

Question 19

How do the otoliths detect gravity?

Answer 19

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

Question 20

How are the hair cells oriented in the utricle compared to the saccule?

Answer 20

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

Question 21

a pure tone looks like what graphically?

Answer 21

a sine wave

Question 22

frequency determines… and depends on…

intensity determiens…. and depends on….

Answer 22

frequency determines pitch and depends on wavelength

intensity determines loudness and depends on amplitude

Question 23

What is intensity measured in?

Answer 23

decibels - remember it’s a log scale!

Question 24

What part of the ear really determines what we hear? Why?

Answer 24

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

Question 25

What are the three mechanisms of impedence matching in the middle ear?

Answer 25

1. the TM is much bigger than the oval window - area ratio
2. the handle of hte malleus is much bigger than the handle of the incus (level ratio)
3. the TM is anchored around the outside so it will buckle more in the middle such that the force is concentrated there

Question 26

Alterations int he impedance matching will result in a deficit of conductive or neurosensory hearing>

Answer 26

conductive

Question 27

What are the two things that affect acoustic impedance in the middle ear?

Answer 27

the middle ear is better or worse at minimizing loss depending on frequency

the two properties associated with this are mass and stiffness (elasticity)

Question 28

Heavier things will responate at __ frequencies

Stiffer things will responate at ___ frequencies

Answer 28

lower

higher

Question 29

What frequency hearing loss will a patient experience in otosclerosis?

Answer 29

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

Question 30

What frequency hearing loss will you have in an otitis media? As the condition worsens?

Answer 30

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

Question 31

At what range of frequencies do humans hear best?

Answer 31

500 Hx to 5 KHz

Question 32

As you move away from the 500 Hz to 5 KHz range, threshold for activation…

Answer 32

goes up

Question 33

Before we reach saturation for audition we reach the…

Answer 33

pain threshold

Question 34

How do audiograms compare the threshold intensity required to detect any given frequency?

Answer 34

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

Question 35

How does a newborn’s range differ from ours?

Answer 35

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

Question 36

How is the basilar membrane arranged? What determines this?

Answer 36

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

Question 37

True or false, the cochlea will conduct the sound in the same way regardless of how it was conducted.

Answer 37

true

Question 38

Why is air conduction better than bone conduction if the cochlea doesn’t care?

Answer 38

amplification delivered by the middle ear makes air conduciton better

Question 39

Traveling waves will always start at the __ and travel towards the ___

Answer 39

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

Question 40

Why do the different regions of the cochlea resonate differently?

Answer 40

number of cells icnreases going towards the apex

stiffness will be greater at the base (resnate higher frequencies)

Question 41

How are the outer hair cells involved in a positive feedback mechanism for hearing and otoacoustic emissions?

Answer 41

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

Question 42

What affect does the outer hair cells’ contractility have on threshold levels?

Answer 42

they amplify the activity of the inner hair cells such that threshold level is lower - doesn’t take as much itnensity for activation

Question 43

How can you utilize otoacoustic emissions (and the non-linearness of the auditory system) clinically?

Answer 43

you can use it to test hearing in infants since they can’t respond to questions

Question 44

WHat produces the endolymph?

Answer 44

the stria vascularis

Question 45

What is the endocochlear membrane potential and K+ concentration? What does this mean for driving force?

Answer 45

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+

Question 46

What transporter in the stria is affected by loop diuretics? What’s the effect?

Answer 46

the Na/K/2Cl transporter

side effects of loop diuretics include hearing loss