The Inner Ear

1. The Inner Ear SPA 4302 Summer 2006

2. INNER EAR Sensory Endorgans encased within very dense bone Two Halves: • ____________--transduces motion and pull of gravity • ____________-transduces sound energy (Both use Hair Cells)

4. Subdivision into spaces containing ___________ (blue), and spaces containing __________ (red)

5. Cochlea is Divided into 3 “Scala” • Scala Vestibuli • __________ Membrane • Scala Media • __________ Membrane • Scala Tympani • ___________ - the opening between 2 outer Scala

6. Fluids filling the Inner Ear • ___________- in S. Vestibuli and S. Tympani • High Sodium / Low Potassium concentrations • Low Voltage (0 to +5 mV) • ___________- in S. Media • High Potassium / Low Sodium concentrations • High Positive Voltage (85 mV)

7. Cross-Section of the Cochlea Third Turn Second Turn First Turn

9. A Cross Section Shows the 3 Scala

12. Within S. Media is the Organ of Corti

14. I = Inner Hair Cells P = Pillar Cells O = Outer Hair Cells D = Deiter’s Cells

15. The Stereocilia on IHCs and OHCs • ________ (at top) • V or W shaped ranks • ________ (at bottom) • straight line ranks

16. Stereocilia bent toward tallest row • ________ flows into cell • ________ flows into cell • Voltage shifts to a less __________ value • More neurotransmitter is released

17. Cochlear Afferent (Sensory) Neurons • __________ (95%) • synapse w/ IHC • 1 IHC to 20 neurons • well myelinated • __________ (5%) • Synapse with OHCs • Many OHCs to 1 neuron • unmyelinated

18. Cochlear Functions • __________- Converting acoustical-mechanical energy into electro-chemical energy. • ___________- Breaking sound up into its component frequencies

19. Development of the Inner Ear • Beginning in week 3, ________________ develops, • Invaginates to form _______________, • Which then closes off, leaving an _________________.

20. Capsule divides into saccular, utricular divisions • ________: cochlea (begins forming in week 6) • ________: semicirc. canals, endolymphatic sac & duct • Organ of Corti forms from week ___ • Inner ear fully formed by ___ weeks

21. Hearing Loss and Disorders of the Inner Ear • Vast majority of SNHL results from inner ear disorder. • Cochlear pts often hear, but cannot distinguish what they hear very clearly: ____________. • Arises from frequency and other distortions associated with changes in inner ear function.

22. Inner Ear Disorders: Prenatal Causes • Genetic mutation/inheritance • Cytomegalovirus (CMV) • __________ • Rubella • Rh incompatibility • __________

23. Anatomical Anomalies Often seen as Bony malformations Examples: Mondini (incomplete cochlea) Enlarged Duct (shown here)

24. Age Effects

25. Noise Damage • Temporary Threshold Shift (TTS) • Permanent Threshold Shift (PTS) • Duration, Timing and Intensity influence • Typical “Noise Notch” often seen between ____________ first. • Notch widens and deepens over time, with hearing loss spreading to adjacent frequencies, and increasing in degree.

26. Ototoxicity Substances poisonous to the ear • Medicines • ___________ antibiotics • ___________ drugs for CA • ___________ • Industrial Chemicals (tolulene, etc) May affect __________ Degree of hearing loss varies Synergy with noise or other ototoxic agents

27. Meniere’s Disease • Really a Syndrome: • _________ Vertigo • Roaring, Low Freq. Tinnitus • Fluctuating ___________ Hearing Loss • Sensation of Aural Fullness • Thought to be produced by ____________________, a condition in which too much endolymph accumulates in the inner ear.