Transcript 10b Central Auditory Pathways

AUDITORY PATHWAYS
& HEARING
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Auditory Projections
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Tonotopic
Organization
of A1
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Medial
Geniculate
Nucleus
Auditory
Cortex
Inferior Colliculus
Cochlear Nucleus
Left Auditory Nerve
Superior
Olive
Right Auditory Nerve
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Cochlea
Auditory Nerve
Cochlear Nucleus
Superior Olive
Medial
Geniculate
Nucleus
Auditory
Cortex
Inferior
Colliculus
Cochlear Nucleus
Left Auditory
Nerve
Inferior
Colliculus
Medial Geniculate
Nucleus
Primary Auditory - A1 (41)
Secondary Auditory - A2 (42)
Superior
Olive
Right Auditory Nerve
Auditory
Pathways
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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
Frequency (Hz)
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Range of Hearing
Range of
speech
sounds
20
50 100
200 500 1000 2000
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 Deafness
Anything up to
but not including
the cochlea
1.Obstructions
2.Damage
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Treating
Conduction
Deafness
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•
•
•
Remove Obstruction
Repair Eardrum
Repair Ossicles
Open Eustacian Tube
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Nerve Deafness
Damage to the Cochlea, Or
Path to Cortex
1. Cilia or Hair Cells
2. Basilar Membrane
3. Auditory Nerve
4. Olive
5. Auditory Tract
6. Inferior Colliculus
7. MGN of Thalamus
8. 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 coiled
And 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 Deafness
Damage to the Cochlea, Or
Path to Cortex
1. Cilia or Hair Cells
2. Basilar Membrane
3. Auditory Nerve
4. Olive
5. Auditory Tract
6. Inferior Colliculus
7. MGN of Thalamus
8. Auditory Projections
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Causes of Type II Nerve
Deafness
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•
•
•
•
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
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