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AUDITORY PATHWAYS & HEARING Anthony J Greene 1 Anthony J Greene 2 Auditory Projections Anthony J Greene 3 Tonotopic Organization of A1 Anthony J Greene 4 Medial Geniculate Nucleus Auditory Cortex Inferior Colliculus Cochlear Nucleus Left Auditory Nerve Superior Olive Right Auditory Nerve Anthony J Greene 5 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 6 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 7 Range of Hearing 20 50 100 200 500 1000 2000 Frequency (Hz) Anthony J Greene 5000 10000 8 Range of Hearing Range of speech sounds 20 50 100 200 500 1000 2000 Frequency (Hz) Anthony J Greene 5000 10000 9 Audiogram Anthony J Greene 10 Audiogram critical for certain consonants Anthony J Greene 11 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 Anthony J Greene 12 Auditory Impairments, Sensory Substitution & Treatments Anthony J Greene 13 Types of Impairment 1. Conduction Deafness 2. Nerve Deafness 3. Cortical Deafness Anthony J Greene 14 Conduction Deafness Anything up to but not including the cochlea 1.Obstructions 2.Damage Anthony J Greene 15 Treating Conduction Deafness • • • • Remove Obstruction Repair Eardrum Repair Ossicles Open Eustacian Tube Anthony J Greene 16 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 Anthony J Greene 17 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. Anthony J Greene 18 Anthony J Greene 19 Treating Type I Nerve Deafness Cochlear Implant 20 Cochlear Implant: Internal Anthony J Greene 21 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 Anthony J Greene 22 Anthony J Greene 23 Anthony J Greene 24 Anthony J Greene 25 Anthony J Greene 26 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 Anthony J Greene 27 Causes of Type II Nerve Deafness • • • • • Degenerative nerve disease Congenital disorder Infection Stroke Trauma Anthony J Greene 28 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 29 Summary of Nerve Deafness • Caused by damage between cochlea and cortex • Cochlear Implants • Stem Cell Research Anthony J Greene 30 Sensory Substitution • ASL: • Closed Captioning Foundation Anthony J Greene 31