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The Auditory

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The Auditory & Vestibular Systems Introduction Sensory Systems Sense of hearing, audition Detect sound Perceive and interpret nuances Sense of balance, vestibular ... – PowerPoint PPT presentation

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Title: The Auditory


1
The Auditory Vestibular Systems
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

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

4
The Nature of Sound
5
The Nature of Sound
6
The Structure of the Auditory System
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

8
The Middle Ear
  • Components of the Middle Ear

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

10
The Inner Ear
  • Anatomy of the Cochlea

11
The Inner Ear
  • Anatomy of the Cochlea

12
The Inner Ear
  • Physiology of the Cochlea
  • Pressure at oval window, pushes perilymph into
    scala vestibuli, round window membrane bulges out

13
The Inner Ear
  • The Organ of Corti

14
The Inner Ear
  • Cilia

15
The Inner Ear
  • Cilia

16
The Inner Ear
17
The Inner Ear
  • Transduction by Hair Cells
  • Sound
  • Basilar membrane upward
  • reticular lamina up
  • stereocilia bends outward

18
The Inner Ear
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

20
The Inner Ear
  • The Basilar Membrane
  • Structural properties Wider at apex, stiffness
    decreases from base to apex

21
The Inner Ear
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

23
Auditory Pathway
24
Auditory Pathway
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

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

27
Encoding Sound Intensity and Frequency
  • Phase Locking
  • Consistent firing of cell at same sound wave
    phase

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 20-2000 Hz
  • Interaural intensity difference 2000-20000 Hz

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

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

31
Mechanisms of Sound Localization
A given binaural neuron indicates the amount of
phase disparity between inputs from the left and
right ear.
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

33
Auditory Cortex
  • Principles in Study of Auditory Cortex
  • Tonotopy, columnar organization of cells with
    similar binaural interaction

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

35
The Vestibular System
36
The Vestibular System
  • The Otolith Organs

37
The Vestibular System
  • The Otolith Organs

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

39
The Vestibular System
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

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

42
The Vestibular System
  • Vestibular Pathology
  • Drugs (e.g., antibiotics) can damage vestibular
    system
  • Effects
  • Trouble fixating on visual targets
  • Walking and standing difficult

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

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

45
  • End of Presentation
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