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CSD9510 > 11 - AR Pathology > Flashcards

11 - AR Pathology Flashcards

1
Q

What is the acoustic reflex activated by?

A
  • loud sound

- tactile stimulation

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2
Q

What is the AR?

A

Acoustic Reflex

-a bilateral reflexive contraction of the ME muscles resulting from sound stimulation of one ear

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3
Q

Which muscle primarily controls the AR in humans?

A

The stapedius muscle

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4
Q

What does the reflexive contraction of the ME muscles do?

A

Stiffens the ME conductive mechanism

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5
Q

Which nerve innervates the stapedius muscle?

A

CN VII (Facial)

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6
Q

The stapedius muscle contraction exerts force on the stapes _____ to normal direction of movement, thereby stiffening the conductive mechanism

A

Perpendicular

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7
Q

The Tensor Tympani muscle may contribute to the acoustic reflex under certain situations. Name 2 things that can activate it.

A
  • acoustic startle response at highest intensities
  • vocalizations
  • facial movements (chewing, yawning)
  • tactile stimulation (ear, face, eye)
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8
Q

What nerve is the Tensor Tympani Muscle innervated by?

A

CN V (Trigeminal)

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9
Q

Where does the Tensor Tympani tendon insert and how does it pull?

A

Inserts at top of manubrium of malleus

-pulls malleus anteriorly medially

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10
Q

What are the 4 main theories as to why we have an acoustic reflex?

A

Interference Theory - attenuates low frequencies to reduce the “upper spread of masking” effects and improve perception of higher frequency components

Desensitization Theory - desensitization to internal body sounds during eating and vocalizations

Injury Prevention Theory - attenuates intense sounds, though this is unlikely due to delay in onset and decay with continuous sound

Multifunctional Theory - combination of all theories

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11
Q

The AR is not useful for “lesions” above where?

A

The lower (auditory) brainstem level

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12
Q

During AR, the Test Ear is the ear with the ______ (tone/probe)

A

Tone

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13
Q

During AR, “ipsi” refers to the the test (stimulus) ear being the ear with the ____ (earphone/probe)

A

Probe

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14
Q

What are the 4 possible AR outcomes (ie. presence and level of AR).

A

Present and normal threshold
Present and elevated threshold
Present and reduced threshold
Absent

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15
Q

Name the 2 abnormal AR threshold results possible

A

Absent AR

Elevated Threshold

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16
Q

Describe a normal AR threshold result

A
  • threshold is usually ~85 dB HL
  • upper limits for normal hearing individual are:
    • 500-2 kHz = 95 dB HL
    • 4 kHz = 105 dB HL
17
Q

What 2 things can we infer if the AR is present?

A
  • normal ME function

- normal - mild SNHL range

18
Q

Name 2 of the 5 reasons an AR might be absent or elevated

A
  • ME disorder
  • SNHL
  • VIIIth nerve pathology
  • VIIth nerve pathology
    CNS dysfunction (brainstem)
19
Q

What does a normal AR threshold indicate?

A
  • reflex at a normal sensation level
  • normal ME and brainstem function
  • abnormalities above brainstem may be present
20
Q

What AR threshold results would you expect to see for a Normal Right Ear and a Left Ear with a Conductive HL?

A

Right Contra - absent
Right Ipsi - present
Left Contra - elevated/absent
Left Ipsi - absent

LE Conductive HL attenuates LE stimulus
LE ME pathology reduces LE ME Ya and limits AR

21
Q

What problem would you expect if all four (RE ipsi and contra, LE ipsi and contra) reflexes were absent?

A

Conductive HL bilaterally

  • bilateral conductive HL attenuates stimulus in both ears
  • bilateral ME pathology reduces ME Ya and limits AR bilaterally
22
Q

For Otosclerosis, what would we expect for:

  • tympanogram shape
  • physical change of ear bones
  • baseline admittance
  • AR threshold
A
  • Tymp: As (shallow peak; usually associated with otosclerosis, but also otitis media)
  • Fixation of stapes footplate
  • Increased ME stiffness and reduced baseline admittance
  • Absent AR (stapes muscle contraction ineffective due to footplate fixation)
23
Q

What would the following results indicate for the right and left ear?

  • Right Ipsi: present
  • Right Contra: present
  • Left Ipsi: absent or elevated
  • Left Contra: absent or elevated
A

Right: Normal hearing
Left: Cochlear HL ( > mild)
-reduced LE cochlear activity

24
Q

What kind of AR threshold results would you expect for:

  • Right: normal hearing
  • Left: cochlear HL (mild)
A

-Right Ipsi: present
-Right Contra: present
-Left Ipsi: present
-Left Contra: present
(sufficient LE cochlear activation and normal ME)

25
Q

True or False: mild cochlear HL bilaterally can still result in present AR thresholds

A

True; there can be sufficient cochlear activation and normal ME function bilaterally

26
Q

If there is >mild cochlear HL bilaterally, what might our AR thresholds show?

A

Right Ipsi: absent or elevated
Right Contra: absent or elevated
Left Ipsi: absent or elevated
Right Contra: absent or elevated

  • Moderate and Severe SNHL bilaterally with sufficient cochlear activation and normal ME = elevated
  • Severe and Profound SNHL bilaterally with insufficient cochlear activation and normal ME = absent
27
Q

CN VIII pathologies: A cerebellopontine angle tumour (acoustic tumour or neuroma) grows the occupy the space between the cerebellum and pons. Would you expect this to cause abnormal results on one or both sides?

A

Abnormal (elevated or absent) results when the ear on the side with the pathology is stimulated

  • elevated = affected side has normal or SNHL, reduced neural input, and normal ME. Unaffected side all normal
  • absent = affected side has normal or SNHL, blocked neural input, and normal ME. Unaffected side all normal
28
Q

Describe how CN VII pathologies affect AR threshold results and why

A
  • abnormal AR outcomes for all probe measures on same side as lesion
  • normal ME function
  • lesion is on the facial nerve in the descending pathway of the AR arc
29
Q

If the Left Ear had normal hearing and the Right Ear had normal hearing, but a CN VII pathology, what AR threshold results would you expect?

A

Right Contra: present
Right Ipsi: absent
Left Contra: absent
Left Ipsi: present

Right ear normal, except for abnormal efferent pathway

30
Q

Brainstem (intra-axial) Pathologies:
If there is a lesion within the brainstem proper, what might we expect to see regarding the crossed and uncrossed pathways?

A

Lesions within the brainstem proper involve the CNS regions of the AR pathway, but can vary in size and location

  • there may be damage to one or both crossed pathways
  • uncrossed pathways may be spared
31
Q

Brainstem (extra-axial) Pathologies:

Where are extra-axial pathologies found and which pathways might they affect?

A
  • lesions are found external to the brainstem proper and can vary in size and location
  • involve crossed and/or uncrossed pathways
  • cortical pathologies do not influence the AR pathways
32
Q

True or False: In a normal auditory system, the stapedius muscle remains contracted with constant stimulation

A

False: stapedius muscle gradually relaxes

  • amount and rate of this reflex adaptation is directly related to the frequency of the activator signal ( >1000 Hz AR decay is considered normal)
  • inversely related to the level (less AR decay as test tone intensity increases)
33
Q

What is abnormally rapid reflex decay associated with?

A

Retrocochlear disorders

34
Q

To measure AR decay, we present a stimulus at a level ____ dB above the acoustic reflex threshold for 10 seconds

A

10 dB above the AR threshold

35
Q

How is abnormal AR decay determined?

A

More than 50% decay in 10 seconds
OR
50% decay in less than 5 seconds
(always retest for reliability)

36
Q

At which frequencies do we test AR decay?

A

500 Hz and 1000 Hz

37
Q

How do we record decay?

A

As the time taken to reach 50% decay

38
Q

Why do patients with CN VIII lesions exhibit high rates of AR adaptation?

A

CN VIII cannot maintain neural firing rate due to pathology

39
Q

Which pathology is more likely to show reflex decay: a cochlear pathology (e.g. Meniere’s) or a retrocochlear pathology (CN VIII)?

A

Retrocochlear lesion

CSD9510 (17 decks)

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