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Anthony J Greene 1 AUDITORY PATHWAYS & HEARING

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Anthony J Greene 1

AUDITORY PATHWAYS & HEARING

Anthony J Greene 2

Anthony J Greene 3

Auditory Projections

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Tonotopic Organization

of A1

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Medial Geniculate Nucleus

Auditory Cortex

Inferior Colliculus

Cochlear NucleusLeft Auditory Nerve Superior

OliveRight Auditory Nerve

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Auditory Pathways

Medial Geniculate Nucleus

Auditory Cortex

Inferior Colliculus

Cochlear NucleusLeft Auditory

Nerve

Superior Olive

Right Auditory Nerve

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Auditory Pathways• Auditory Nerve - Axons from hair cells• Cochlear Nucleus - Sends information from the

auditory nerve to the Superior Olive and to the Inferior Colliculus

• Superior Olive - Analogous to the Optic Chiasm - information from both ears crosses over to be sent to both hemispheres

• Inferior Colliculus - Analogous to the Superior Colliculus for vision - Orienting and reflexive localization -- recent studies show multimodal neurons in the colliculus which share visual and auditory information for orientation movements

• Medial Geniculate Nucleus (MGN) Relays information from the SO to A1

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Range of Hearing

20 50 100 200 500 1000 2000 5000 10000

Frequency (Hz)

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Range of Hearing

Range of speech sounds 20 50 100 200 500 1000 2000 5000 10000

Frequency (Hz)

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Audiogram

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Audiogram

critical for certain consonants

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Hearing Loss• Conduction Deafness - any damage to the middle ear

which impairs hearing

• Nerve Deafness or Presbicusis- Effects High Frequencies - Less elasticity in the Basilar membrane - Loss of nutrients to cochlea - Cumulative effects of noise

• Noise Exposure - Effects High Frequencies - Both Sudden and prolonged exposure

• When high Frequency hearing is impaired speech perception becomes increasingly difficult

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Auditory Impairments, Sensory Substitution

& Treatments

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Types of Impairment

1. Conduction Deafness

2. Nerve Deafness

3. Cortical Deafness

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Conduction DeafnessAnything up to but not including the cochlea

1.Obstructions

2.Damage

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Treating Conduction

Deafness

• Remove Obstruction

• Repair Eardrum

• Repair Ossicles

• Open Eustacian Tube

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Nerve DeafnessDamage to the Cochlea, Or Path to Cortex1. Cilia or Hair Cells2. Basilar Membrane3. Auditory Nerve4. Olive5. Auditory Tract6. Inferior Colliculus7. MGN of Thalamus8. Auditory Projections

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Causes of Type I Nerve Deafness

• Presbycusis – Old Ear -- High Frequency hearing loss

• Noise Induced Hearing Loss: Also effects high frequencies – Damage to cilia or Bassilar membrane -- Tinitus

• Infection of Cochlea – Damage to cilia• Menier’s Disease: Excessive fluid pressure

in Cochlea damages Organ of Corti.

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Treating Type I Nerve Deafness

Cochlear Implant

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Cochlear Implant: Internal

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Cochlear Implant

• Recall that the cochlea is coiledAnd that the basillar membrane selects frequencies

• The electrode has multiple stimulation points that selectively activate nerves at the appropriate places

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Nerve DeafnessDamage to the Cochlea, Or Path to Cortex1. Cilia or Hair Cells2. Basilar Membrane3. Auditory Nerve4. Olive5. Auditory Tract6. Inferior Colliculus7. MGN of Thalamus8. Auditory Projections

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Causes of Type II Nerve Deafness

• Degenerative nerve disease

• Congenital disorder

• Infection

• Stroke

• Trauma

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Treating Type II Nerve Deafness

• No cure at present

• Stem cells research is designed to allow new nerve growth in damaged areas.

• Has already worked with Parkinson’s and Tourrette’s

• Should work for vision, audition, Alzheimers, Epilepsy, stroke, etc.

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Summary of Nerve Deafness

• Caused by damage between cochlea and cortex

• Cochlear Implants

• Stem Cell Research

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Sensory Substitution

• ASL:

• Closed Captioning Foundation