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Paul Faure

October 8 , 2013 Psych 3A03: Audition Outer and Middle Ear How Sound Is Heard - We have seen how airborne vibrations are generated, propagated, and dissipated by the environment - Next we will see how these mechanical vibrations are converted into hydrodynamic (fluid) vibrations before encoded as electrochemical (neural) impulses - Acoustic energy is collected (funnelled) by the outer ear and then impinges on the eardrum (tympanic membrane) - This mechanical energy is transmitted to the middle ear via a chain of small bones, the middle ear ossicles - The middle ear converts mechanical vibrations into fluid pressure changes inside the inner ear (cochlea) Outer Ear - Pinna - Ear canal Transfer of Sound Energy to Ear - Lateral portion is considered to be the external ear Middle Ear - Eardrum - Malleus - Incus - Stapes - Eustachian tube (cavity that connects to the nasal pharynx) Outer and Middle Ear - Pressure changes in cochlear fluids are used to generate neural impulses (action potentials) for analysis by CNS Inner Ear - Semicircular canals - Vestibule - Cochlea - Vestibular neurons on the cochlea and vestibule forming the auditory nerve Outer and Middle Ears - Outer and middle ears allow for very efficient transfer of the acoustic stimulus (sound energy into neural energy) - Outer and middle ears have a number of functions, but perhaps their most important function is to overcome the impedance mismatch between sound energy traveling in air and sound energy transmitted to fluid filled inner ear - Outer and middle ears also protect the inner ear from damage and excessive changes in environment (e.g. temperature, humidity and especially pressure changes) - Tympanic membrane also protects middle ear from foreign (invading) bodies - Refer to appendix E and appendix F to review basic neural anatomy/physiology, and learn hearing research tools Outer Ear - Air pressure collected by pinna (pinnae) - Pinnae connected to tympanum via external auditory meatus (opening) and external auditory canal (the canal itself) - Deep center portion of pinna (1-2 cm diameter; ca. 2.5 kHz resonance) is called the bowl or concha (cave) - The concha leads to the external auditory meatus (5-7 mm diameter; ca. 5kHz resonance) - The external auditory canal is 2-3 cm long - Only mammals have pinna, and only those with good high frequency hearing have mobile pinnae - Resonance of concha and external auditory canal produce 10-20 dB gain in acoustic pressure from 1.5 to 7kHz - Concha and auditory canal cause sounds to interfere with each other so there is a gain in pressure Human Pinnae Shapes and Sizes - Individual differences in shapes and sizes of the pinnae Anatomy of the Human Pinna - Outer helix - Antihelix fold - Tragus - Antihelix Sound Features Altered b
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