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CHAPTER 15
Central Auditory Nervous System
Central Nervous System
Structures
• Nucleus = a group of nerve cell bodies
• Fiber Tract = a group of axons
Major Components of the Central
Auditory Nervous System (CANS)
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VIIIth cranial nerve
Cochlear Nucleus
<Trapezoid Body>
Superior Olivary Complex
Lateral Lemniscus
Inferior Colliculus
Medial Geniculate Body
Primary Auditory Cortex
Brainstem
Mid-brain
Thalamus
Temporal Lobe
Mid-Saggital View of Brain
4th Ventricle
Corpus
Callosum
Cerebellum
Thalamus
Pons
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MedGen Body
Inf Coll
Lat Lemn
SOC
Coch Nuc
VIIIth CN
Neural Web-Sites
http://rprcsgi.rprc.washington.edu/
neuronames/hierarchy.html
http://www.ets.uidaho.edu/med532/start.htm
Section Thru Brainstem Shows
Cochlear Nucleus
The Superior Olivary Complex
Connections To the Superior
Olivary Complex
Superior Olivary Processing
Supports Localization
• Lateral SO-- Interaural Intensity Differences
• Medial SO-- Interaural Time Differences
(These are the two primary acoustic cues for
localizing sounds)
Dorsal (back) Side of Brainstem
• Thalamus
(medial geniculate)
• Inferior Colliculus
• 4th Ventricle
• Area of Pons
Inferior Colliculus
Thalamus in Purple
Auditory Radiations Connect
• Medial Geniculate
Body (in purple)
to
• Primary Auditory
Cortex (in blue)
Lateral-Superior view of brain
Primary Auditory Cortex (AI):
superior surface of the temporal lobe
6 Cortical Layers
• Thalamic inputs >IV
• project to pyramidal cells
in layer III
• Divergence from III
– within AI
– other cortical areas
– contra AI
• V and VI >>thalamus &IC
Cortical Neurons
• Tonotopically and Spatiotopically organized
• Highly Adaptable
• Sensitive to CHANGES in Frequency and
Intensity
– Coding virtual pitch
– demodulating complex signals (e.g. speech)
Cortical Processing
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Pattern Recognition
Duration Discrimination
Localization of Sounds
Selective Attention
Cerebral Dominance/Laterality
• Language Processing in the left hemisphere.
(Remember the right ear has the strongest
connections to the left hemisphere)
• Most people show a right-ear advantage in
processing linguistic stimuli
Neurophysiological Measures
• Gross Evoked Potentials-- Voltage changes
in response to auditory stimulation recorded
from the scalp
• Single-Unit Measures-- Voltage (or other)
changes recorded within a neuron
Auditory Evoked Potentials
• Recorded in different time intervals
(“epochs”) following a sound
• Earlier epochs come from lower in the
system
• Later epochs come from higher in the
system
Examples of AEP Epochs
• Electrocochleography-- within 5 milliseconds
• Auditory Brainstem Response-- thru 10 ms
• Middle Latency Response-- thru 75 ms
• Auditory Late Response-- thru 200 ms
Auditory Brainstem Response
IV
Amplitude (V)
III
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V
II
Amp V
Wave V Latency
Time (ms)
0
10
GENERATORS of ABR WAVES
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II
III
IV
V
= Distal VIIIth nerve
= Medial VIIIth nerve
= Cochlear Nucleus
= Superior Olivary Complex
= Lateral Lemniscus &
Inferior Colliculus
The Acoustic Reflex
Afferent:
Efferent:
• VIIIth nerve
• VIIth nerve nucleus
• Cochlear Nucleus
• VIIth nerve
• Superior Olivary
Complex
• Stapedius muscle