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Anthony J Greene 5
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
Anthony J Greene 7
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
Anthony J Greene 9
Range of Hearing
Range of speech sounds 20 50 100 200 500 1000 2000 5000 10000
Frequency (Hz)
Anthony J Greene 12
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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Types of Impairment
1. Conduction Deafness
2. Nerve Deafness
3. Cortical Deafness
Anthony J Greene 15
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
Anthony J Greene 18
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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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
Anthony J Greene 28
Causes of Type II Nerve Deafness
• Degenerative nerve disease
• Congenital disorder
• Infection
• Stroke
• Trauma
Anthony J Greene 29
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.
Anthony J Greene 30
Summary of Nerve Deafness
• Caused by damage between cochlea and cortex
• Cochlear Implants
• Stem Cell Research