Auditory System

Question 1

What is the function of the outer ear

Answer 1

Collection of sound; protection, funneling of sound, and spectral filtering for sound localization

Question 2

What is the function of the inner ear

Answer 2

Transduction of sound; functions as the sensory transducer of sound-driven vibrations, gravity, and acceleration into neuronal signals via inner hair cells

Question 3

What is the function of the middle ear

Answer 3

Conduction/Amplification of sound; serves as an impedance matching device, allowing for adequate transfer of energy from air-borne sound to fluid-filled cochlea

Question 4

What is the route of conduction of sound from the middle to the inner ear?

Answer 4

Tympanum –> malleus –> incus –> stapes –> oval window –> scala vestibuli –> helicotrema –> scala tympani –> round window

Question 5

What is the stapedius reflex?

Answer 5

Contraction of the stapedius in response to high intensity sounds or just before speaking

Question 6

What is the route of the stapedius reflex?

Answer 6

Loud sound travels to auditory nerve –> V. Cochlear nucleus –> S. Olivary nucleus –> facial motor nucleus, which release ACh to cause stapedius muscle contraction

Question 7

How does sound transduction occur?

Answer 7

Pressure oscillations in the cochlea induce movement (vibration of the organ of corti); different parts of the basilar membrane move optimally at different frequencies of sound

Question 8

What is endolymph

Answer 8

Contains high K+ and low Na+ and protein. +80mV, secreted from stria vascularis via Na/K

Question 9

What is perilymph

Answer 9

Similar to interstitial fluid, with high Na+ and Cl-, low protein

Question 10

What is the difference between perilymph and endolymph

Answer 10

Perilymph has high Na+, endolymph has low Na+; both have low protein; perilymph fills the vestibuli and tympani while endolymph fills the cochlear duct (media)

Question 11

What is the result of the Rinne test if there is unilateral conduction hearing loss?

Answer 11

Bone louder than airborne

Question 12

What is the result of the Weber test if there is unilateral conduction hearing loss?

Answer 12

Louder on affected side

Question 13

Where does sound travel faster, water or air?

Answer 13

WATER, but most of it gets rejected

Question 14

Which bone of the middle ear is referred to as the “anvil”

Answer 14

incus

Question 15

Which bone of the middle ear is referred to as the “stirrup”

Answer 15

stapes

Question 16

Which bone of the middle ear is referred to as the “hammer”

Answer 16

Malleus

Question 17

What is the innervation of the middle ear?

Answer 17

A branch of the facial nerve and a branch of the trigeminal nerve

Question 18

What is the musculature of the middle ear

Answer 18

Stapedius muscle and tensor tympani muscle

Question 19

What do the facial nerve branch and stapedius muscle act on?

Answer 19

The stapes; nerve innervates the stapedius muscle

Question 20

What do the trigeminal nerve branch and tensor tympani muscle act on?

Answer 20

tympanic membrane (muscle travels through the proximal portion of the eustachian tube); nerve innervates the tensor tympani

Question 21

How does contraction of the middle ear muscles (stapedius and tensor tympani) affect amplification

Answer 21

Decreases amplification of the movements of the middle ear ossicles (increased impedance)

Question 22

What is the purpose of contraction of the middle ear muscles

Answer 22

Protection against loud sounds, especially at lower frequencies to allow detection of higher frequencies

Question 23

Where does the perilymph drain?

Answer 23

From the perilymph duct into the CSF of the subarachnoid space

Question 24

What is the helicotrema

Answer 24

Apex of the cochlear labyrinth. The hair cells near this area best detect low frequency sounds.

Question 25

What are the 3 fluid filled chambers of the cochlea?

Answer 25

Scala vestibuli, scala tympani, and scala media (cochlear duct)

Question 26

What is the organ of corti

Answer 26

Site of mechano-electrical transduction

Question 27

What is the frequency discrimination in humans?

Answer 27

0.2%

Question 28

What three factors does frequency discrimination depend upon?

Answer 28

1. tonotopic organization of hair cells 2. membrane potential 3. cilia length

Question 29

What is place theory?

Answer 29

The PLACE along the basilar membrane where the optimal hair cell discharge is attained; explains how frequencies of sound are coded

Question 30

What causes the bending of cilia?

Answer 30

Basilar membrane moving up and down, resulting in the organ of corti sliding in and out relative to the tectorial membrane

Question 31

Does the basilar membrane go up or down during excitation? inhibition?

Answer 31

Excitation - up | inhibition - down

Question 32

How does inner hair cell transduction work?

Answer 32

K+ and Ca++ influx results in glutamate release, which acts on AMPA-type glutamate receptors of cochlear nerve fibers

Question 33

What is the auditory pathway, starting from the dorsal acoustic stria

Answer 33

Cochlear nuclei --> dorsal acoustic stria --> contralateral to the nucleus of lateral lemniscus (pons) --> inferior colliculus (midbrain) --> medial geniculate nucleus (midbrain) --> primary auditory cortex (AKA temporal gyrus, Heschl's gyrus, area 41)

Question 34

What is the auditory pathway, starting from the trapezoid body

Answer 34

Cochlear nuclei --> trapezoid body --> bilateral superior olivary nuclei (pons) --> bilateral nuclei of lateral lemniscus --> bilateral inferior colliculus --> unilaterally to medial geniculate nucleus --> primary auditory cortex

Question 35

What is the auditory pathway, starting from the intermediate acoustic stria

Answer 35

Cochlear nuclei --> intermediate acoustic stria --> nucleus of the lateral lemniscus --> inferior colliculus --> medial geniculate nucleus --> primary auditory cortex

Question 36

What are the 5 main classifications of deafness?

Answer 36

Conduction, sensorineural, neural, central, genetic

Question 37

What is the sound intensity level equation?

Answer 37

L = 20log(P/Pref)

Question 38

What is the decibel loss equation?

Answer 38

-20log(Ppt/Pnl)

Question 39

``` A noise level of 20 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off ```

Answer 39

A) Quiet room

Question 40

A noise level of 60 decibels would best equate to which of the following? A) Personal music player at high volume B) A busy street C) An ordinary spoken conversation D) Aircraft taking off

Answer 40

C) an ordinary spoken conversation

Question 41

``` A noise level of 70 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off ```

Answer 41

B) a busy street

Question 42

``` A noise level of 100 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off ```

Answer 42

C) a pneumatic drill

Question 43

``` A noise level of 105 decibels would best equate to which of the following? A) Personal music player at high volume B) A busy street C) An ordinary spoken conversation D) Aircraft taking off ```

Answer 43

A) Personal music player at high volume

Question 44

``` A noise level of 110 decibels would best equate to which of the following? A) Personal music player at high volume B) A busy street C) An ordinary spoken conversation D) Aircraft taking off ```

Answer 44

D) Aircraft taking off

Question 45

What is BAER used for?

Answer 45

Brain stem auditory evoked response is used to assess auditory function in infants and in general in patients not able to respond

Question 46

What are the steps in audiometry?

Answer 46

1. present different tones to each ear 2. increase intensity to threshold 3. Hearing ability at given frequency is given as threshold pressure compared to normal population and is presented as hearing loss in decibels

Question 47

What is the amount of decibel loss that is considered abnormal?

Answer 47

> -20 dB loss

Question 48

What would be the decibel loss if a patient's threshold pressure is 1000x normal?

Answer 48

60

Question 49

What is conduction deafness?

Answer 49

Decreased vibrations to the basilar membrane and decreased air conduction; bone conduction is okay

Question 50

Which frequency range is affected in conduction deafness?

Answer 50

Broad range, but especially low frequencies

Question 51

Which frequency range is affected in conduction deafness?

Answer 51

Broad range, but especially low frequencies

Question 52

What are possible causes of conduction deafness?

Answer 52

Foreign objects/wax in the ear canal, otitis media, otosclerosis

Question 53

What is otosclerosis?

Answer 53

A cause of conduction deafness; overgrowth of temporal bone around oval window, limiting stapes movement

Question 54

What are the treatments for conduction deafness?

Answer 54

Remove cause, surgery, hearing aids

Question 55

What are the presynaptic changes during temporary conduction hearing loss?

Answer 55

Decrease in VGlut1 in auditory nerve endings and SV size

Question 56

What are the postsynaptic changes during temporary conduction hearing loss

Answer 56

Thicker PSD, increased GluA3 AMPARs - decrease in vesicular glutamate transporter postsynaptic densities altered as well

Question 57

What are presynaptic changes when hearing is restored after temporary conduction hearing loss

Answer 57

Increased SV size and density in auditory nerve endings

Question 58

What are the postsynaptic changes when hearing is restored after temporary conduction hearing loss

Answer 58

Thicker and larger PSD, increased GluA3, fewer GluA2 AMPARs

Question 59

What is sensorineural deafness

Answer 59

Loss of both air and bone conduction

Question 60

What frequencies are affected in sensorineural deafness

Answer 60

High frequencies

Question 61

What are some causes of sensorineural deafness?

Answer 61

Chronic loud sounds, aminoglycoside antibiotics (parental use of streptomycin, neomycin, gentamicin, esp. long duration use), quinine, prolonged high doses of aspirin, vaccines (rubella), old age (presbyacusis)

Question 62

What is the treatment for sensorineural deafness?

Answer 62

Hearing aids (microphone-amplifier-speaker)

Question 63

Hair cell loss can be associated with which classification of deafness?

Answer 63

Sensorineural

Question 64

What is the purpose of cochlear implants?

Answer 64

They are important for severe and complete hearing loss; they are multi-channel stimulatory devices placed in the cochlear duct

Question 65

What is neural deafness?

Answer 65

Unilateral, sensorineural deafness

Question 66

What are the most common causes of neural deafness?

Answer 66

Schwannoma or acoustic neuroma of auditory nerve in the internal auditory canal

Question 67

What is central deafness

Answer 67

Deafness that may manifest as auditory hallucinations (schizophrenia, temporal lobe damage, seizures), pure word deafness, auditory agnosia, and amusia (right hemisphere)

Question 68

What are possible causes of central deafness?

Answer 68

Lesion in the CNS causing abnormal processing of auditory signals (very rare) OR bilateral brainstem injury (inferior colliculus) OR cortical deafness (bilateral embolic stroke Heschl's gyri)

Question 69

What is the prevalence of genetic deafness?

Answer 69

1/1,000

Question 70

Which genes are affected in genetic deafness?

Answer 70

Connexins 26 and 30, SLC26A4, and mitochondrial genes