CSD 3103 anatomy of speech and hearing mechanisms Hearing mechanisms Fall 2008

1. CSD 3103anatomy of speech and hearing mechanismsHearing mechanismsFall 2008 The Inner Ear

2. The major divisions of the inner ear • The vestibular system • The cochlea • The osseous or bony labyrinth • The membranous labyrinth

3. Location of the inner ear within the skull

4. Cross section of the inner ear

5. The bony labyrinth

6. The bony labyrinth

7. The cochlea Modiolus Internal auditory meatus Auditory nerve Facial nerve

8. Modiolus and internal auditory meatus

9. The cochlea • Scala vestibuli • Scala tympani • Scala media • Helicotrema • Perilymph

10. The membranous labyrinth The membranous labyrinth in relation to the bony labyrinth

11. The membranous labyrinth Endolymph Semicircular canals Utricle Saccule Scala media

12. The membranous labyrinth Ampullae Crista ampularis Ductus Reuiens

13. The cochlear duct

14. Cross section of the cochlea Eighth Nerve Vestibular branch Acoustic branch Base Apex Modiolus Helicotrema Scala Vestibuli, Tympani and Media Basilar Membrane Reissner’s Membrane Spiral Lamina

15. Spiral lamina

16. Cochlear partitions An “unrolled” cochlea, showing the relationships among the three scalae

17. Cochlear partitions

18. Cochlear cross-section

19. Cochlear duct and the organ of corti

20. Cochlear duct and the organ of corti

21. organ of corti

22. organ of corti

23. Inner hair cell

24. Outer hair cell

25. Path of vibration through the cochlea Vibrations are transmitted across scala media into scala tympani

26. Mass-action flow through the cochlea Inward movement of the stapes footplate causes perilymph to flow up scala vestibuli, through the helicotrema, and down scala tympani, where the round window is distended

27. Displacement of the basilar and tectorial membranes The vertical displacement of the basilar and tectorial membranes produces a shearing force on the cilia of the hair cells

28. Basilar membrane displacement Relative motion between the basilar and tectorial membranes places a shearing force on the stereocilia so they are bent away from the modiolus when the cochlear duct is displaced upward

29. Cochlear function

30. Movement of the basilar membrane Schematic representation of the cochlea with the vestibule cut away. Arrows show the effects of a compressional sound wave produced by the stapes. Example of the position of a portion of the basilar membrane in 3 successive instants during sinusoidal stimulation.

31. Traveling wave Characteristics of the traveling wave generated by a 200 Hz stimulus peaking at a distance of about 29mm from the base of the cochlea

32. Traveling wave envelopes for three different frequencies

33. The traveling wave Schematic of amplitude patterns of traveling waves for sinusoids of various frequencies

34. Traveling wave response as a function of frequency

35. Place coding mechanism of the cochlea

36. Place-by-frequency conversion along the basilar membrane

37. Organization of the cochlea Tonotopic organization relates to the placement of auditory neurons in a particular structure (in this case, the cochlea) according to their responsiveness to specific frequencies