Middle Ear Structure-Function & Pathology

Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Lecture 12. Middle Ear Structure-Function & Pathology I. The Middle ear A. Anatomy of the Middle Ear Figure 12.1 A schematic ‘coronal’-section of the human auditory periphery Image removed due to copyright considerations. Source: Anne Green drawing in Kiang NYS, Peake WT. "Physics and Physiology of Hearing." In Stevens' Handbook of Experimental Psychology. Edited by Atkinson R. C., Herrnstein R. J., Lindzey G., and Luce R. D. New York: John Wiley & Sons, 1988. page 1 Adapted from from Adapted B Helix (pf) Fossa of Helix Antihelix (pf) Cymba (concha) A Cavum (concha) Antitragus Crus helias A' Tragus L Lobule (pf) Mid-concha position Ear canal entrance position Ear canal insert position Eardrum position Lecture 12 The cat external ear (Rosowski JJ, Carney LH, Peake WT. (1988). The radiation impedance of the external ear of cat: Measurements and applications. Journal of the Acoustical Society of America 84:1695-1708.) Acoustics of Speech & Hearing 6.551/HST.714J 5 mm PINNA FLANGE MEDIAL SUPERIOR CONCHA POSTERIOR CANAL Courtesy of Acoustical Society of America. Used with permission. page 3 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Figure 12.3 Two Views of the Human Tympanic membrane (the eardrum) Image removed due to copyright considerations. Source: Schuknecht, H. F. Pathology of the ear. Cambridge: Harvard University Press, 1974. page 4 Lecture 12 Acoustics of Speech & Hearing Figure 12.4 A Medial View of the Human Middle Ear -TM -ossicles Malleus with Umbo Incus Stapes with footplate -middle-ear muscles Tensor Tympani ) Stapedius Muscle -mastoid air spaces -Tympanic cavity -Eustachian Tube -VII (Facial) Nerve 6.551/HST.714J Image removed due to copyright considerations. Source: Henson, O. W. "Comparative anatomy of the middle ear." In Handbook of Sensory Physiology: The Auditory System. Edited by Kiedel W. D., Neff W. D. 1974, pp. 39-110. Figure 12.5 The Three Human Ossicles Image removed due to copyright considerations. Source: Henson, O. W. "Comparative anatomy of the middle ear." In Handbook of Sensory Physiology: The Auditory System. Edited by Kiedel W. D., Neff W. D., 1974, pp. 39-110. page 5 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Figure 12.6: A cast of the Human Inner ear: After Schuchnect 1974 Image removed due to copyright considerations. Source: Schuknecht, H. F. Pathology of the ear. Cambridge: Harvard University Press, 1974. page 6 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Figure 12.7: A horizontal section through the human ear: Source: Schuknecht, H. F. Pathology of the ear. Cambridge: Harvard University Press. 1974. Image removed due to copyright considerations. B. There is a wide variation in the form and function of the ossicles and middle-ear air spaces. Fig 12.8: (Source: Rosowski, J. J. The Evolutionary Biology of Hearing. New York: Springer-Verlag, 1992, pp. 625-631.) page 7 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Image removed due to copyright considerations. Figure 12.9 Image removed due to copyright considerations. The middle ears of mammals are different from those of other terrestrial vertebrates in that other vertebrates (bird’s reptiles and amphibians) have a single ossicle, a curved out tympanic membrane, one or no middle-ear muscle and a middle-ear cavity that is less well defined. (Source: Rosowski, J. J. "The middle and external ears of terrestrial vertebrates as mechanical and acoustic transducers." In Sensors and Sensing in Biology and Engineering. Edited by Barth, F. G., Humphrey J. A. C., and Secomb T. W. New York: Springer-Verlag, 2003, pp.59-69.) Fig 12.10: Middle-Ear System Function: Stapes Velocity / Sound Pressure in Ear canal page 8 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Rosowski 2003 C. There is also a wide variation in the hearing range of different animals page 9 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Figure 12.11: Pure-Tone Audiograms (Threshold sound level vs frequency contours for the human (Sivian & White 1932) domestic cat (Heffner and Heffner 1985),bat (Long & Schnitzler 1975), pigeon (Heinz et al. 1985) and Bull Frog (Megela-Simmons 1987). The abscissa is tone frequency. The left ordinate is the threshold sound pressure in dB SPL. The right ordinate is the threshold in pascals. (Rosowski 2003) page 10 Fluid-filled cochlea Acoustic shield between oval and round windows POW PRW Middle-ear air space VOW VRW Bone Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Image removed due to copyright considerations. Source: Merchant, S. N., and J. J. Rosowski. " Auditory Physiology (Middle-Ear Mechanics)." In Surgery of the Ear. 5th ed. Edited by A. J. Gulya, and M. E. Glasscock, III (Hamilton, Ontario, B. C. Decker, 2002) pp. 59-82. Ossicularly Coupled Sound in the Normal Ear PWD ≈ P S and Acoustically Coupled Sound (POW – PRW )=∆P Image removed due to copyright considerations. Source: Merchant, S. N., and J. J. Rosowski. "Auditory Physiology (Middle-Ear Mechanics)." In Surgery of the Ear. 5th ed. Edited by A. J. Gulya, and M. E. Glasscock, III (Hamilton, Ontario, B. C. Decker, 2002), pp. 59-82. In Cases of Severe Ossicular Disruption Acoustic Coupling Limits the hearing loss : (Merchant & Rosowski 2002) A: Interrupt I-S Joint B: Lost TM, malleus & incus page 12 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J . Image removed due to copyright considerations Source: Merchant, S. N., and J. J. Rosowski. "Auditory Physiology (Middle-Ear Mechanics)." In Surgery of the Ear. 5th ed. Edited by A. J. Gulya, and M. E. Glasscock, III (Hamilton, Ontario, BC Decker, 2002), pp. 59-82. �� page 13 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J Type IV Tympanoplasty: Use of Acoustic Shielding to Manipulate Acoustic Coupling by Increasing the Window Pressure Difference: Merchant SN and Rosowski JJ. 2002 Image removed due to copyright considerations. Source: Merchant, S. N., and J. J. Rosowski. "Auditory Physiology (Middle-Ear Mechanics)." In Surgery of the Ear. 5th ed. Edited by A. J. Gulya, and M. E. Glasscock, III (Hamilton, Ontario, BC Decker, 2002), pp. 59-82. �� Image removed due to copyright considerations. Source: Merchant, S. N., and J. J. Rosowski. "Auditory Physiology (Middle-Ear Mechanics)." In Surgery of the Ear. 5th ed. Edited by A. J. Gulya, and M. E. Glasscock, III (Hamilton, Ontario, BC Decker, 2002), pp. 59-82. �� page 14 Lecture 12 Acoustics of Speech & Hearing E. Another reconstructive surgery; the stapedectomy 6.551/HST.714J Image removed due to copyright considerations. Source: Rosowski, J. J., and S. N. Merchant. "Mechanical and Acoustic Analysis of Middle Ear Reconstruction." American Journal of Otology 16 (1995): 486-497.�� UT PEC + _ MIDDLE EAR� TWO PORT VS US + + FS PC Š Š A FP:1 ZC PEC = Ear Canal Sound Pressure UT = TM Volume Velocity FS = Force on Stapes/Prosthesis VS = Stapes/Prostehesis Velocity AFP = Area of the Footplate/Prosthesis PC = Sound Pressure in the Cochlea US = Stapes/Prosthesis Volume Velocity page 15 Lecture 12 Acoustics of Speech & Hearing 6.551/HST.714J ZC = Cochlear Acoustic input Impedance Predicted Variations in Hearing Level with Different Prosthesis Cross-Sectional Areas Image removed due to copyright considerations. Source: Rosowski, J. J., and S. N. Merchant. "Mechanical and Acoustic Analysis of Middle Ear Reconstruction." American Journal of Otology 16 (1995): 486-497. Rosowski & Merchant 1995 If we define the Source Impedance as the impedance on the Left (input side) of the transformer when the source is turned off, and the Load Impedance as the impedance loading the Right (output side) of the transformer, then the Maximum Available Power reaches the load when the transformer matches the two impedances. Matching occurs when the two impedances are complex conjugates. page 16