SM_28b: Ear Function and Testing

Question 1

Lateral portion of external auditory canal is composed of ____, while medial portion of external auditory canal is composed of ____

Answer 1

Lateral portion of external auditory canal is composed of cartilage, while medial portion of external auditory canal is composed of bone

Question 2

Describe innervation of external auditory canal

Answer 2

Innervation of external auditory canal

• Lesser occipital nerve (C2)
• Auriculotemporal nerve (V3)
• Facial nerve sensory branch
• Greater auricular nerve (C2, C3)
• Auricular branch of vagus nerve

Question 3

Outer ear functions include ____, ____, and ____

Answer 3

Outer ear functions include amplification / filtering, protection, and localization

• Amplification / filtering: filters sound to external auditory canal, 20 dB amplification, strongest at 4000 Hz
• Localization: interaural time difference, interaural intensity difference (Head Shadow effect)

Question 4

Tympanic membrane parts include ____ and ____

Answer 4

Tympanic membrane parts include pars tensa and pars flaccida

• Para tensa: how eardrum grows, vibrates ossicles
• Pars flaccida: prevents eardrum from collapsing on itself

Question 5

Describe the middle ear

Answer 5

Middle ear

• Mucous membrane lining
• Tympanic membrane separates it from external auditory canal
• Eustachian tube connects it to nasopharynx
• Also connected to mastoid air cells

Question 6

Label the middle ear structures

Answer 6

Middle ear structures

Question 7

Middle ear muscles include the ____ and ____

Answer 7

Middle ear muscles include the stapedius and tensor tympani

• Stapedius: attaches to stapes, makes ossicles less likely to move, contracts in response to loud sounds / chewing / speaking, facial (CN VII)
• Tensor tympani: helps open Eustachian tube

Question 8

____ matchmaking occurs in the middle ear

Answer 8

Impedance matchmaking occurs in the middle ear

• Fluid in cochlea has high impedence compared to air in external / middle ear
• Ossicles overcome this with impedance matching and increasing sound pressure
• Multiple mechanisms: area ratio of tympanic membrane to oval window is 20:1, lever action of ossicles

Question 9

Inner ear is composed of ____ and ____ halves, both of which use ____

Answer 9

Inner ear is composed of vestibular and cochlear halves, both of which use hair cells

• Vestibular: transduces motion and pull of gravity
• Cochlear: transduces sound energy

Question 10

Scala vestibuli and scala tympani have high ___ and low ___, while the scala media has low ___ and high ___

Answer 10

Scala vestibuli and scala tympani have high Na and low K, while the scala media has low Na and high K

(ionic gradient acts as a battery)

Question 11

Stapes movement sets up vibration in the ____

Answer 11

Stapes movement sets up vibration in the scala media

• Fluid wave starts at the oval window and scala vestibuli
• Travels from the base to apex of cochlea
• Continues back down through scala tympani to the round window

Question 12

____ is in the scala media

Answer 12

Organ of Corti is in the scala media

Question 13

Describe the process of a traveling sound wave

Answer 13

Traveling sound wave

1. Fluid wave displaces basilar membrane
2. Resonates in specific areas based on frequency
3. Appropriate hair cells stimulated: inner hair cells created signal, outer hair cells amplify

Question 14

Describe cochlear tuning

Answer 14

Cochlear tuning

• Tuning exists through auditory system
• Basilar membrane has varying width and stiffness
• Base of cochlea has stiff basilar membrane so high frequency
• Apex of cochlea has flaccid basilar membrane so low frequency

Question 15

Base of cochlea has ___ basilar membrane so frequency is ___

Answer 15

Base of cochlea has stiff basilar membrane so frequency is high

Question 16

Apex of cochlea has ___ basilar membrane so frequency is ___

Answer 16

Apex of cochlea has flaccid basilar membrane so frequency is low

Question 17

____ are found on inner and outer hair cells

Answer 17

Stereocilia are found on inner and outer hair cells

• Outer hair cells: V or W shaped ranks
• Inner hair cells: straight line ranks

Question 18

Inner hair cell activation alters ____

Answer 18

Inner hair cell activation alters firing rate

Question 19

Inner hair cells stimulate ____

Answer 19

Inner hair cells stimulate spiral ganglion cells

• Housed in Rosental’s Canal
• Afferent projections make cochlear nerve

Question 20

Cochlear nerve stimulates ____

Answer 20

Cochlear nerve stimulates spiral ganglion cells

(normally stimulated by inner hair cells)

Question 21

Describe the central auditory nervous system pathway

Answer 21

Central auditory nervous system pathway

1. Brainstem
2. Midbrain
3. Thalamus
4. Temporal lobe

Question 22

Cortical auditory processing functions in ____, ____, ____, and ____

Answer 22

Cortical auditory processing functions in pattern recognition, duration discrimination, localization of sounds, and selective attention

Question 23

Semicircular canals are for ____ movements, while the saccule / utricle are for ____ accelerations

Answer 23

Semicircular canals are for rotational movements, while the saccule / utricle are for linear accelerations

Question 24

Head rotation causes a fluid shift in the ____, pushing against the ____, causing the hair cells to ____

Answer 24

Head rotation causes a fluid shift in the semicircular canal, pushing against the cupula, causing the hair cells to depolarize

Question 25

Describe ear testing

Answer 25

Ear testing

Question 26

Conductive hearing loss is \_\_\_

Answer 26

Conductive hearing loss is when sound is blocked on its way to the cochlea

Question 27

Sensorineural hearing loss is \_\_\_\_

Answer 27

Sensorineural hearing loss is when the cochlea and/or auditory nerve are not working

Question 28

Air conduction is \_\_\_\_

Answer 28

Air conduction is the normal auditory pathway

Question 29

Bone conduction is \_\_\_\_

Answer 29

Bone conduction is when vibrations on bone directly transmit to cochlea

Question 30

Describe the Weber test

Answer 30

Weber test * Vibrating tuning fork is placed on middle of the forehead or vertex * Normal hearing: Equal sound in both ears * Sensorineural hearing loss: sound lateralizes towards the good ear (away from bad ear) * Conductive hearing loss: sound lateralizes towards bad ear

Question 31

Sensorineural hearing loss on the Weber test is when \_\_\_\_

Answer 31

Sensorineural hearing loss on the Weber test is when sound lateralizes towards the good ear (away from bad)

Question 32

Conductive hearing loss on the Weber test is when \_\_\_\_

Answer 32

Conductive hearing loss on the Weber test is when sound lateralizes toward the bad ear

Question 33

Describe the Rhinne test

Answer 33

Rhinne test * Vibrating tuning fork placed on mastoid bone (bone conduction) and moved to outside of ear (air conduction) when patient can no longer hear sound * Normal hearing: air conduction is louder than bone (+ Rhinne) * Sensorineural hearing loss: air conduction is louder than bone (unless "dead ear") * Conductive hearing loss: bone conduction is louder than air (- Rhinne)

Question 34

Sensorineural hearing loss on Rhinne test is when \_\_\_\_

Answer 34

Sensorineural hearing loss on Rhinne test is when air conduction is louder than bone (unless "dead ear")

Question 35

Conductive hearing loss on Rhinne test is when \_\_\_\_

Answer 35

Conductive hearing loss on Rhinne test is when bone conduction is louder than air (- Rhinne)

Question 36

Describe conventional audiometry (audiogram)

Answer 36

Conventional audiometry (audiogram) * Pure tones at different frequencies, using air and bone conduction * Increasing sound levels (dB) with worsening hearing loss * Higher on chart is better: lower on chart (higher dB) is worse hearing

Question 37

Describe profound hearing loss

Answer 37

Profound hearing loss * Poor word understanding * Distortion * No role for hearing aids * Cochlear implants

Question 38

Tympanometry is used to ___ and \_\_\_

Answer 38

Tympanometry is used to check pressure in ear and help establish Eustachian tube function (pressures should be the same on either side of eardrum)

Question 39

Describe speech testing

Answer 39

Speech testing * Speech reception thresholds: when sound is recognized as speech * Word recognition scores: ability to understand what is being spoken: closed set (4 options), open set (all words)

Question 40

Describe acoustic reflex testing

Answer 40

Acoustic reflex testing * Response of stapedius muscle to loud sound * Reflex arc through auditory (VIII), brainstem, and facial (VII) bilaterally * Tone presented to each ear and response measured in both * Absent in severe hearing loss / stapes fixation

Question 41

Otoacoustic emissions are \_\_\_\_

Answer 41

Otoacoustic emissions are sounds given off by the inner ear when the cochlea is stimulated by sound * Vibration produces a nearly inaudible sound that echoes back into the middle ear * Sound can be measured with a small probe inserted into ear canal * When click sound is applied to ear, it clicks back * Absence of otoacoustic emissions: block in air conduction or within cochlea * May be present with deficits of auditory nerve (VIII)

Question 42

Describe audiograms in children by age

Answer 42

Audiograms in children by age * Age 0-5 months: behavioral observation audiometry - eye widening, startle, quieting * Age 6 months - 2 years: visual reinforcement audiometry - toy lights up if they turn towards sound * Age 2-5 years: conditioned play audiometry - listening game (putting toys in a bucket)

Question 43

Auditory brainstem response is \_\_\_

Answer 43

Auditory brainstem response is evoked potential generated by brief click * Amplitude is averaged and charted against time * Done in young or developmentally delayed children or those with severe / profound hearing loss during cochlear implant workup