1. The Auditory & Vestibular Systems
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2. Introduction Sensory Systems Sense of hearing, audition Detect sound
Perceive and interpret nuances
Sense of balance, vestibular system
Head and body location
Head and body movements
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3. The Nature of Sound Sound Audible variations in air pressure
Sound frequency: Number of cycles per second expressed in units called Hertz (Hz)
Cycle: Distance between successive compressed patches
Range: 20 Hz to 20,000 Hz
Pitch: High and Low
Intensity: Difference in pressure between compressed and rarefied patches of air
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4. The Nature of Sound
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5. The Nature of Sound
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6. The Structure of the Auditory System
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7. The Structure of the Auditory System
Auditory pathway stages
Sound waves
Tympanic membrane
Ossicles
Oval window
Cochlea fluid
Sensory neuron response
Brain stem nuclei output
Thalamus to MGN to A1
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8. The Middle Ear
Components of the Middle Ear
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9. The Middle Ear Sound Force Amplification by the Ossicles
Pressure: Force by surface area
Greater pressure at oval window than tympanic membrane, moves fluids
The Attenuation Reflex
Response where onset of loud sound causes tensor tympani and stapedius muscle contraction
Function: Adapt ear to loud sounds, understand speech better
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10. The Inner Ear
Anatomy of the Cochlea
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11. The Inner Ear
Anatomy of the Cochlea
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12. The Inner Ear Physiology of the Cochlea
Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out
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13. The Inner Ear
The Organ of Corti
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14. The Inner Ear
Cilia
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15. The Inner Ear
Cilia
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16. The Inner Ear
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17. The Inner Ear Transduction by Hair Cells Sound:
Basilar membrane upward
reticular lamina up
stereocilia bends outward
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18. The Inner Ear
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19. The Inner Ear The Innervation of Hair Cells
One spiral ganglion fiber: One inner hair cell, numerous outer hair cells
Amplification by Outer Hair Cells
Function: Sound transduction
Motor proteins: Change length of outer hair cells
Prestin: Required for outer hair cell movements
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20. The Inner Ear The Basilar Membrane
Structural properties: Wider at apex, stiffness decreases from base to apex
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21. The Inner Ear
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22. Central Auditory Processes
Auditory Pathway
More synapses at nuclei than visual pathway, more alternative pathways
Anatomy
Dorsal cochlear nucleus, ventral cochlear nucleus, superior olive, inferior colliculus, MGN, lateral lemniscus, auditory nerve fiber
Primary pathway: Ventral cochlear nucleus to superior olive to inferior colliculus to MGN to auditory cortex
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23. Auditory Pathway
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24. Auditory Pathway
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25. Central Auditory Processes
Response Properties of Neurons in Auditory Pathway
Characteristic frequency
Frequency at which neuron is most responsive
Response
More complex and diverse on ascending auditory pathway in brain stem
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26. Encoding Sound Intensity and Frequency
Encoding Information About Sound Intensity
Firing rates of neurons
Number of active neurons
Stimulus Frequency, Tonotopy, Phase Locking
Frequency sensitivity: Basilar membrane
Frequency: Highest at base, lowest at cochlea apex
Tonotopy: Systematic organization of characteristic frequency within auditory structure
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27. Encoding Sound Intensity and Frequency
Phase Locking
Consistent firing of cell at same sound wave phase
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28. Mechanisms of Sound Localization
Techniques for Sound Localization
Horizontal: Left-right, Vertical: Up-down
Localization of Sound in Horizontal Plane
Interaural time delay: Time taken for sound to reach from ear to ear
Interaural intensity difference: Sound at high frequency from one side of ear
Duplex theory of sound localization:
Interaural time delay: Hz
Interaural intensity difference: Hz
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29. Mechanisms of Sound Localization
The Sensitivity of Binaural Neurons to Sound Location
Monaural: Sound in one ear
Binaural: Sound at both ears
Superior olive: Cochlear nuclei input to superior olive, greatest response to specific interaural delay
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30. Mechanisms of Sound Localization
Delay Lines and Neuronal Sensitivity to Interaural Delay
Sound from left side, activity in left cochlear nucleus, sent to superior olive
Sound reaches right ear, activity in right cochlear nucleus, first impulse far
Impulses reach olivary neuron at the same time summation action potential
Localization of Sound in Vertical Plane
Sweeping curves of outer ear
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31. Mechanisms of Sound Localization
A given binaural neuron indicates the amount of phase disparity between inputs from the left and right ear.
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32. Auditory Cortex Acoustic Radiation
Axons leaving MGN project to auditory cortex via internal capsule in an array
Structure of A1 and secondary auditory areas: Similar to corresponding visual cortex areas
Neuronal Response Properties
Frequency tuning: Similar characteristic frequency
Isofrequency bands: Similar characteristic frequency, diversity among cells
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33. Auditory Cortex Principles in Study of Auditory Cortex
Tonotopy, columnar organization of cells with similar binaural interaction
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34. The Vestibular System Importance of Vestibular System
Balance, equilibrium, posture, head, body, eye movement
The Vestibular Labyrinth
Lateral line Organs
Small pits or tubes
Function
Sense vibration or pressure changes
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35. The Vestibular System Head Rotation Head Angle Linear Acceleration
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36. The Vestibular System
The Otolith Organs
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37. The Vestibular System
The Otolith Organs
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38. The Vestibular System The Semicircular Canals
Function: Detect head movements
Structure
Crista: Sheet of cells where hair cells of semicircular canals clustered
Ampulla: Bulge along canal, contains crista
Cilia: Project into gelatinous cupula
Kinocili oriented in same direction so all excited or inhibited together
Semicircular canals: Filled with endolymph
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39. The Vestibular System
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40. The Vestibular System Push-Pull Activation of Semicircular Canals
Three semicircular canals on one side
Helps sense all possible head-rotation angles
Canal: Each paired with another on opposite side of head
Push-pull arrangement of vestibular axons: Rotation causes excitation on one side, inhibition on the other
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41. The Vestibular System The Vestibulo-Ocular Reflex (VOR)
Function: Line of sight fixed on visual target
Mechanism: Senses rotations of head, commands compensatory movement of eyes in opposite direction
Connections from semicircular canals, to vestibular nucleus, to cranial nerve nuclei  excite extraocular muscles
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42. The Vestibular System Vestibular Pathology
Drugs (e.g., antibiotics) can damage vestibular system
Effects:
Trouble fixating on visual targets
Walking and standing difficult
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43. Concluding Remarks Hearing and Balance
Nearly identical sensory receptors (hair cells)
Movement detectors: Periodic waves, rotational, and linear force
Auditory system: Senses external environment
Vestibular system: Senses movements of itself
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44. Concluding Remarks Hearing and Balance
Auditory Parallels Visual System
Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code
Convergence of inputs from lower levels  Neurons at higher levels have more complex responses
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45. End of Presentation
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