2. 2
Introduction
Auditory messages are conveyed to the
brain via two types of pathway:
• primary auditory pathway which
exclusively carries messages from the
cochlea
• non-primary pathway (also called the
reticular sensory pathway) which carries
all types of sensory messages
3. Primary auditory cortex
• The primary auditory cortex is located in
the temporal area within the lateral
sulcus.
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4. Primary auditory cortex
• The major cortical target of the
neurons in the medial geniculate
nucleus.
• Receives point-to-point input from
the ventral division of the medial
geniculate complex.
• It contains a precise tonotopic map.
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5. Belt areas
• The belt areas of the auditory
cortex receive more diffuse
input from the belt areas of the
medial geniculate complex.
• Less precise in their tonotopic
organization.
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6. Primary auditory cortex
• The primary auditory cortex has a
topographical map of the cochlea.
• The cochlea has already
decomposed the acoustical
stimulus so that it is arrayed
tonotopically along the length of
the basial membrane.
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7. Binaural properties
• The neurons in one stripe are
excited by both ears: EE cells.
• The neurons in the next stripe are
excited by one ear and inhibited by
the other ear: EI cells.
• The EE and EI stripes alternate.
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8. Primary auditory pathway
anatomy
• The first relay of the primary
auditory pathway occurs in
the cochlear nuclei in the brain
stem (type I spiral ganglion axons).
• At this level an important decoding
of the basic signal occurs: duration,
intensity and frequency.
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9. Primary auditory pathway
anatomy
• The second major relay in the
brain stem is in the superior
olivary complex.
• The majority of the auditory
fibres synapse there having
already crossed the midline.
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10. Primary auditory pathway
anatomy
• A third neuron carries the
mesage up to the level of
the inferior
colliculus (mesencephalus).
• These two relays play an
essential role in the localisation
of sound.
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11. Primary auditory pathway
anatomy
A last relay, before the cortex,
occurs in the medial geniculate
body (thalamus).
An important integration
occurs: preparation of a motor
response (vocal response).
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12. Primary auditory pathway
anatomy
The final neuron of the primary
auditory pathway links the thalamus
to the auditory cortex.
The message, already largely
decoded, is recognized, memorized
and perhaps integrated into a
voluntary response.
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14. Non-primary pathways
• The main function of these
pathways is to select the type of
sensory message to be treated first.
• These pathways are connected to
wake and motivation centers and
vegetative, hormonal systems.
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15. Non-primary pathways
• The first relay locates in
the cochlear nuclei (brainstem).
• From here, the small fibers rejoin
the ascending reticular pathway.
• In the reticular pathway of the
brainstem and the mesencephalus,
several synapses occur.
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17. Non-primary pathways
After the reticular formation:
• the non-primary pathway leads to
the non-specific thalamus
• then to the polysensory cortex
Conscious perception requires the
integrity of both types of pathways.
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