2. Physiology of auditory system References:  Guyton & Hall  Review of medical physiology (Ganong) Dr. Mohammadi

3. The Ear  Houses two senses  Hearing  Equilibrium (balance)  Receptors are mechanoreceptors

4. Anatomy of the Ear

5. The External Ear

6. Middle Ear

7.  Two tubes are associated with the inner ear  The opening from the auditory canal is covered by the tympanic membrane  The auditory tube connecting the middle ear with the throat (Eustachian tube) Allows for equalizing pressure during yawning or swallowing

9. Impedance matching ↑17 times in force ↑1.3 times in force Total: 17 × 1.3 = 22

10. Amplification

11. Attenuation reflex  Contraction of the stapedius muscle pulls the handle of the stapes outward  Contraction of the tensor tympani muscle pulls the malleus inward  Increase in ossicular system rigidity  Reducing the ossicular conduction of low frequency sound  Function (Protection & Masking)

12. Inner Ear

15.  Sound  Range: 20 Hz to 20,000 Hz  Pitch: High pitch = high frequency; low frequency = low pitch  Intensity: High intensity louder than low intensity

16. Tonotopic maps on the basilar membrane

18. Travelling wave in the basilar membrane

20. Organ of Corti

24. n = 12000 n = 3500

28. Transduction by hair cells

32. Central auditory system

34. Mechanisms of sound localization  Localization of sound in vertical plan

35. Mechanisms of sound localization (continued )  Superior olivary complex  Medial superior olive (Time delay)  Lateral superior olive (Intensity difference)

38. Auditory cortex  Superior temporal gyrus (Brodmannś area 41)

39.  Complete bilateral removal of the auditory cortex:  Detection of sounds remains intact  Greatly reduce ability to discriminate different sound pitches and specially patterns of sound  Loss of almost all ability to detect the sounds direction  Greatly reduces one's sensitivity for hearing  Destruction of one side:  Only slightly reduces hearing in the opposite ear  Loss of ability to detect the sounds direction  Lesions that affect the auditory association areas:  Loss of ability to interpret the meaning of the sound

40. Damage to the cochlea Drug sensitivity of the organ of Corti Otosclerosis Audiogram in nerve deafnessAudiogram in conduction deafness

41. Ludwig van Beethoven Around 1796, by the age of 26, Beethoven began to lose his hearing. By 1814 however, Beethoven was almost totally deaf.