Transcript Chapter 11: The Auditory and Vestibular Systems

Bear: Neuroscience: Exploring the
Brain 3e
Chapter 11: The Auditory
and Vestibular Systems
Slide 1
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 2
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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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Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Structure of the Auditory System
Auditory System
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Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 5
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Middle Ear
Components of the Middle Ear
Slide 6
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 7
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Inner Ear
Anatomy of the Cochlea
Perilymph: Fluid in scala vestibuli and scala
tympani
Endolymph: Fluid in scala media
Endocochlear potential: Endolymph electric
potential 80 mV more positive than perilymph
Slide 8
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Inner Ear
Physiology of the Cochlea
Pressure at oval window, pushes perilymph
into scala vestibuli, round window
membrane bulges out
The Response of Basilar Membrane to Sound
Structural properties: Wider at apex,
stiffness decreases from base to apex
Research: Georg von Békésy
Endolymph movement bends basilar
membrane near base, wave moves
towards apex
Slide 9
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Inner Ear
The Organ of Corti and Associated Structures
Slide 10
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Inner Ear
Transduction by
Hair Cells
Research: A.J.
Hudspeth.
Sound: Basilar
membrane
upward,
reticular
lamina up and
stereocilia
bends outward
Slide 11
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 12
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 13
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 14
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 15
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
Encoding Sound Intensity and
Frequency
Phase Locking
Consistent firing of cell at same sound
wave phase
Slide 16
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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: 200020000 Hz
Slide 17
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 18
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 19
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 20
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
Auditory Cortex
Principles in Study of Auditory Cortex
Tonotopy, columnar organization of cells
with similar binaural interaction
The Effects of Auditory Cortical Lesions and
Ablation
Lesion in auditory cortex: Normal auditory
function
Lesion in striate cortex: Complete
blindness in one visual hemifield
Different frequency band information:
Parallel processing, localization deficit
Slide 21
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 22
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Vestibular System
The Otolith Organs
Slide 23
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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
Slide 24
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 25
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Vestibular System
Central Vestibular Pathways
Slide 26
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 27
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
The Vestibular System
Vestibular Pathology
Drugs can damage vestibular system
Effects:
Trouble fixating on visual targets
Walking and standing difficult
Slide 28
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
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
Slide 29
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
Concluding Remarks
Hearing and Balance (Cont’d)
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
Slide 30
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
End of Presentation
Slide 31
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins