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inner ear anatomy.docx

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Paul Faure

October 9 , 2013 Psych 3A03: Audition Inner Ear Anatomy Sound Features Altered by Head and Body - Pinnae reflect sounds depending on the location - Reflect sounds in a frequency specific matter - Pinna is a filter Function of Outer Ear - Impinging sounds are altered in amplitude and time by head and torso - Small time delays are created for high frequency sounds diffracted by head - Main function is the amplification of air pressures that reach tympanic membrane (i.e. amplification of acoustic energy for middle ear) Transduction from Outer to Inner Ear - Once an acoustic stimulus has been filtered by the pinna and it reaches the tympanic membrane, it could be transmitted to the middle ear via 3 pathways: 1. Bone conduction 2. Middle ear air cavity: airborne sounds directly vibrate dense fluid behind oval window in inner ear (problem: impedance mismatch and simultaneous) 3. Middle ear ossicles: vibrations could transverse the tympanic cavity via ossicular chain (bones provide impedance coupling) Tympanic Membrane - Malleus: first middle ear ossicles also know as the hammer - Light weight mass behind the tympanic membrane as to vibrate more efficiently - Arm of the malleus (manubrium) contacts the tympanic membrane - Point of the concavity of the tympanic membrane is known as the umbo - Membrane has concavity and is oval shaped - Radial fibres coming of the membrane - Composed of tissue layers (radial and circular fibers) – thin but tough enough to withstand changes in pressure - 2cm volume - Connects to 1 middle ear bone (malleus)] - Connects to manubrium of malleus - Umbo portion of tympanic membrane has maximal concavity Gross Auditory Anatomy - Most mass in the epitympanic recess Tympanic Anatomy - Facial nerve - Stapedial tendon - Round window: bulges when stapes pushes on the round window - Head of stapes - Manubrium - Rich supply of blood vessels Eustachian Tube - Auditory tube dump into nasopharynx - For efficient transmission of vibrations, middle ear cannot be closed system - Harder to push if it were a closed system as it does not allow the tympanic membrane to vibrate freely at its natural frequency, increasing force as the membrane is displaced - Otherwise changes in the atmospheric pressure would cause pressure build ups or reductions in tympanum - Eustachian tube allows for equalization of outer and middle ear air pressures - Ear drums push out when we reach higher altitude as the surrounding pressure is decreasing while the internal pressure remains equal and is higher relative to surrounding pressure - Yawning allows to equal the ambience and internal pressure thanks to your
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