Physiology Of Hearing

1. PHYSIOLOGY OF HEARING Crisbert I. Cualteros, M.D.

19. - axis of rotation:  line from short process of incus to neck of malleus MIDDLE EAR

20. MIDDLE EAR CONDUCTION A. Problem – transmission of sound between 2 99.9% reflected 0.1 % transmitted IMPEDANCE MATCHING 20-35 dB loss    different media (air  liquid)

21. MIDDLE EAR CONDUCTION B: TRANSDUCER MECHANISM 1. ratio of drum/ footplate area vibrating TM 55 sq. mm. foot plate 3.5 sq. mm. = 17 (25 to 30 dB) ______________ ______________ =

22. MIDDLE EAR CONDUCTION B. TRANSDUCER MECHANISM 2. Lever mechanism Length long process malleus Length long process incus ______________________________ =1.3 (2.5 dB)

26. Middle ear conduction

27. INTRINSIC MUSCLES OF THE MIDDLE EAR Tensor Tympani Stapedius

28. Sound  EAC  Middle Ear  Inner Ear (Footplate)

30. INNER EAR CONDUCTION C. This results in side to side motion of the hair cells in relation to the tectorial membrane in which they are embedded . D. This shearing action initiates a local electrical potential, COCHLEAR MICROPHONIC, which trigger a nerve impulse.

31. INNER EAR CONDUCTION E. Portion of cochlear stimulated High Frequency  Lower hair cells Low Frequency  Apical cells F. Loudness - number of elements firing

33. Conscious auditory pathway

35. auditory pathway