Topic Fifteen - Cochlear and Retrocochlear Loss

Question 1

What is a motor loss and what are some common pathologies within this category?*

Answer 1

• A motor loss occurs when there is absence / dysfunction of the OHCs with no IHC dysfunction
• Results from disruption to MET or EMT processes

Causes of MET damage:
- Noise trauma
- Ototoxic drugs
- Mechanical biasing of hydrostatic / osmotic imbalances

Causes of EMT damage
- Salicylates
- Excessive efferent neuron activity

Question 2

What is a sensory loss and what are some common pathologies within this category?*

Answer 2

• A sensory hearing loss occurs when there is damage to the inner hair cells
• Dysfunction can occur in three different ways

1. The inner hair cell itself
2. The dendrites connecting to the inner hair cells
3. The synapse between the IHC and the primary afferent neurons: neurotransmitter release or neurotransmitter reception

It is uncommon to have a pure sensory loss, except in the case of auditory neuropathy.

Question 3

What is a mixed loss and some common pathologies within this category?*

Answer 3

• A mixed loss is an impairment of both the IHCs and OHCs

Common causes:
- Ototoxic drugs (aminoglycoside antibiotics, cisplatin)
- Reduction of the driving voltage for the hair cell receptor currents
- Morphological disruption

Question 4

What is the battery loss?*

Answer 4

• Stria vasculairs dysfunction
• Stria is responsible for creating the endocochlear potential which is the driving force for potassium
• Dysfunction can cause both IHC and OHC damage

Question 5

What is the bias loss?*

Answer 5

A mechanical bias of the hair bundles by osmotic or hydrostatic pressures

Question 6

What is the block loss?*

Answer 6

A “block” of the MET channels or the primary afferent synapse by drugs or overstimulation

Question 7

What is the bundle loss?*

Answer 7

Activation of the crossed olivo-cochlear bundle

Question 8

Identify and discuss retrocochlear pathologies

Answer 8

Vestibular Schwannomas
- Hearing loss results from the disruption/blocking of the neural signal traveling to the brain and/or disruption to the blood supply to the cochlear

Multiple Scelerosis
- Demyelinating disease of the CNS
- Hearing loss, vertigo, diplopia, sensory / motor abnormalities
- Pure-tone thresholds are not often affected, if does occur its usually mild
- Deficits on temporal processing tasks
- Localisation abilities are impaired

Cortical Deafness
- Bilateral damage to the primary auditory cortex
- ABR and OAEs normal
- Unable to interpet auditory stimuli

Question 9

What pattern would we expect to see in the tuning curve of a sensory loss?

Answer 9

• Elevation across the entire frequency range
• Because there is no mechanical involvement, there is no impact to the frequency tuning, nonlinear compression and distortion tone.