THE AUDITORY SYSTEM.pptx

THE AUDITORY SYSTEM UNO, VICTOR KANU NEUROANATOMY  ANATOMY AND FUNCTION The auditory system is built to allow us to hear. It is remarkable for its sensitivity  It is especially important in humans because it provides the sensory input necessary for speech recognition. Sound...

THE AUDITORY SYSTEM UNO, VICTOR KANU NEUROANATOMY  ANATOMY AND FUNCTION The auditory system is built to allow us to hear. It is remarkable for its sensitivity  It is especially important in humans because it provides the sensory input necessary for speech recognition. Sound waves converge through the pinna and outer ear canal to strike the tympanic membrane The vibrations of this membrane are transmitted by way of three ossicles (malleus, incus, and stapes) in the middle ear to the oval window, where the sound waves are transmitted to the cochlear duct.  Two small muscles can affect the strength of the auditory signal: the tensor tympani, which attaches to the eardrum, and the stapedius muscle, which attaches to the stapes.  These muscles may dampen the signal; they also help prevent damage to the ear from very loud noises.  The inner ear contains the organ of Corti within the cochlear duct.  As a result of movement of the stapes and tympanic membrane, a traveling wave is set up in the perilymph within the scala vestibuli of the cochlea.  The human cochlea contains more than 1 5,000 hair cells. These specialized receptor cells transduce mechanical (auditory)stimuli into electrical signals.  The traveling waves within the perilymph stimulate the organ of Corti through the vibrations of the tectorial membrane against the kinocilia of the hair cells  The mechanical distortions of the kinocilium of each hair cell are transformed into depolarizations, which open calcium channels within the hair cells. Influx of calcium, after opening of these channels, evokes release of neurotransmitter, which elicits a depolarization in peripheral branches of neurons of the cochlear ganglion. As a result, action potentials are produced that are transmitted to the brain along axons that run within the cochlear nerve.  AUDITORY PATHWAY 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  The Structure of the Auditory System Auditory pathway stages Sound waves Tympanic membrane Ossicles Oval window Cochlea fluid Sensory neuron response Brain stem nuclei output Thalamus to MGN to A1  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  TYPES OF IMPAIREMENT Conduction Deafness Nerve Deafness Cortical Deafness  Treating Conduction Deafness  Remove Obstruction  Repair Eardrum  Repair Ossicles  Open Eustacian Tube  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  CAUSES OF TYPE 1 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 TREATMENT OF TYPE 1 NERVE DEAFNESS: COCHLEA IMPLANT  CAUSE OF TYPE 11 NERVE DEAFNESS Degenerative nerve disease Congenital disorder Infection Stroke Trauma  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 Should work for vision, audition, Alzheimers, Epilepsy, stroke, etc.