1 Organ of Corti

2 Organ of Corti (limbus)

3 Organ of Corti (tectorial memb.)

4 Organ of Corti (inner hair cells)

5 Organ of Corti (outer hair cells)

6

7 Organ of Corti (spriral lamina)

8 Organ of Corti (habenula perforata)

9 Organ of Corti (supporting cells)

10 Organ of Corti (basilar membrane)

11 Organ of Corti (VIIIth nerve)

12

13 More on Cells Hair Cells Outer Hair Cells Inner Hair Cells Supporting Cells (modiolus to stria vascularis) Vestibular Lip Border Cells of Held Inner Phalangeal Cells Rods of Corti (Pillar Cells) Dieters Cells Hensons Cells Claudius and Boettcher Cells

14 Insert zemlin page 471

15 Cross section showing hair cells and supporting cells Note: modiolus is to the right of slide

16 Inner Hair Cells Inner Hair Cells (see previous slide) Jug shaped Larger than OHCs Single Row 3000 to 4000 in number Innervated by both afferent and efferent fibers IHC cilia 50 to 70 cilia per cell in U shaped configuration. Cilia not embedded in tectorial membrane

17 Outer Hair Cells Outer Hair Cells (see previous slide) Tube shaped Smaller than IHCs 3 rows except at apical end where it increases to 4 and then 5 rows 12,000 to 13,000 in number Innervated by both afferent and efferent fibers OHC cilia 58 cilia at apical end to 150 per cell at basal end in W or V shaped configuration. Cilia embedded in tectorial membrane

18 Cilia Photo showing U shaped configuration of IHC (top) and W or V shaped configuration of OHC (bottom)

19

20 Hair Cell Structures

21 Hair Cell (stereocilia)

22 Hair Cell (dendrite)

23 Hair Cell (synaptic cleft)

24 Hair Cell (cuticle)

25 Hair Cell (reticular lamina)

26 Hair Cell (photo) Outer Hair cells showing the stereocilia, reticular lamina and cuticle.

27 Hair Cell (efferent axon)

28 Cross-section of the auditory nerve

Mapping of frequency to place along the basilar membrane preserved in central auditory nervous system fiber CF Tonotopicity in the auditory nerve Base: narrow and tight Apex: wide and looseHair cells Basilar membrane Auditory Nerve Fiber Bundle High frequency fibers: outer auditory nerve Low frequency fibers: inner auditory nerve

30 Auditory Pathways

31 Auditory Pathways

32 Auditory Pathways

33

34 Effects of decusation

35 StructureFunction/Description IHC to Auditory Nerve Fiber1st synapse located in the cochlea Cochlear Nucleus2nd synapse (1st central way station) Superior Olivary Complex3rd synapse, Convergence of inputs from two ears, Delay line, localization Inferior Colliculi4th synapse, multi-sensory integration Medial Geniculate Body5th synapse, located in the thalamus Auditory Cortex6th synapse Central auditory system

36 Sagittal view of the brain

37 Primary auditory cortex is tonotopically organized

8000 Hz fiber CF Normal Hair cell death, 1-2 kHz Plasticity: flexibility, the ability to adapt to new situations. Auditory Cortex Tonotopically organized

39 Central auditory pathways: review

40 Acoustic Reflex Arc Acoustic reflex: 1)Contraction of the stapedius and tensor tympani muscles occurs at high intensity levels 2)The response is bilateral 3)Some functions: Protection from intense sounds Smoothing of the frequency response of the outer and middle ears

41 Acoustic Reflex Arc Afferent Efferent (ipsilateral pathway) Efferent (contralateral pathway) STIMULUS Midline of the brain

42 Inner Ear Fluids

43 Blood Supply

44 Summary