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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 system Head and body location Head and body movements. The Nature of Sound . Sound Audible variations in air pressure

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introduction
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

Psychology 355

the nature of sound
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

Psychology 355

the nature of sound4
The Nature of Sound

Psychology 355

the nature of sound5
The Nature of Sound

Psychology 355

the structure of the auditory system7
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

Psychology 355

the middle ear
The Middle Ear

Components of the Middle Ear

Psychology 355

the middle ear9
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

The Middle Ear

Psychology 355

the inner ear
The Inner Ear

Anatomy of the Cochlea

Psychology 355

the inner ear11
The Inner Ear

Anatomy of the Cochlea

Psychology 355

the inner ear12
The Inner Ear

Physiology of the Cochlea

Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out

Psychology 355

the inner ear13
The Inner Ear

The Organ of Corti

Psychology 355

the inner ear14
The Inner Ear

Cilia

Psychology 355

the inner ear15
The Inner Ear

Cilia

Psychology 355

the inner ear16
The Inner Ear

Psychology 355

the inner ear17
The Inner Ear

Transduction by Hair Cells

Sound:

Basilar membrane upward

reticular lamina up

stereocilia bends outward

Psychology 355

the inner ear18
The Inner Ear

Psychology 355

the inner ear19
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

Psychology 355

the inner ear20
The Inner Ear

The Basilar Membrane

Structural properties: Wider at apex, stiffness decreases from base to apex

Psychology 355

the inner ear21
The Inner Ear

Psychology 355

central auditory processes
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

Psychology 355

auditory pathway
Auditory Pathway

Psychology 355

auditory pathway24
Auditory Pathway

Psychology 355

central auditory processes25
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

Psychology 355

encoding sound intensity and frequency
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

Psychology 355

encoding sound intensity and frequency27
Encoding Sound Intensity and Frequency

Phase Locking

Consistent firing of cell at same sound wave phase

Psychology 355

mechanisms of sound localization
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

Psychology 355

mechanisms of sound localization29
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

Psychology 355

mechanisms of sound localization30
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

Psychology 355

mechanisms of sound localization31
Mechanisms of Sound Localization

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

Psychology 355

auditory cortex
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

Psychology 355

auditory cortex33
Auditory Cortex

Principles in Study of Auditory Cortex

Tonotopy, columnar organization of cells with similar binaural interaction

Psychology 355

the vestibular system
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

Psychology 355

the vestibular system35

Head Rotation

Head AngleLinear Acceleration

The Vestibular System

Psychology 355

the vestibular system36
The Vestibular System

The Otolith Organs

Psychology 355

the vestibular system37
The Vestibular System

The Otolith Organs

Psychology 355

the vestibular system38
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

Psychology 355

the vestibular system39
The Vestibular System

Psychology 355

the vestibular system40
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

Psychology 355

the vestibular system41
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

Psychology 355

the vestibular system42
The Vestibular System

Vestibular Pathology

  • Drugs (e.g., antibiotics) can damage vestibular system
  • Effects:
    • Trouble fixating on visual targets
    • Walking and standing difficult

Psychology 355

concluding remarks
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

Psychology 355

concluding remarks44
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

Psychology 355

end of presentation
End of Presentation

Psychology 355