Auditory Pathway

Question 0

Inner Hair Cells

Connectivity?

Answer 0

about 3,500 per ear

Connectivity: Divergent = 1:Many (1IHC: Up to 30, avg. 8 spiral ganglions)

responsible for coding frequency with little or no loss of information

highly redundant system

Question 1

Auditory Pathway

Answer 1

starts with two types of Hair cells in the Cochlea:

inner hair cells and outer hair cells

Question 2

Outer Hair Cells

Connectivity?

Answer 2

• about 12,000 per ear
• Connectivity: Convergent, Many:1 (Avg ~20 OHC: 1 Spiral Ganglion)
• cannot encode detailed frequency info, but can coney some amplitude info

Question 3

Spiral Ganglions

Answer 3

axons of which form Auditory Nerve

also called Auditory Nerve Fibers

Question 4

NOTE: no ______ in Cochlea, but can get ______ from downstream Superior Olive

Answer 4

Lateral Inhibition

Negative Feedback (Inhibition)

Question 5

Cochlear Nucleus

Answer 5

in Medulla

Monaural site (left Cochlear Nucleus receives from left ear only, right from right only)

Question 6

Each Spiral Ganglion has up to…

Answer 6

…. 5 branches that synapse onto different Cochlear Nucleus cells

begin sub-pathways for different information

Question 7

sequence of Action Potentials from a single Spiral Ganglion might be:

3

Answer 7

1) Faithfully reproduced by a “Primary Like” Cochlear Nucleus cell (e.g. for preserving Tonotopic Map)
2) Transformed into a continually increasing graded response by a “Build-Up” cell (e.g. for amplitude)
3) transformed into a single onset signal by an “Onset” Cochlear Nucleus cell (e.g. for Localization)

Question 8

Superior Olive

in?

critical for?

Answer 8

also in Medulla

Some Cochlear Nucleus axons cross over to contra-lateral Superior Olive, others to ipsi-lateral

this is the first BIAURAL SITE along pathway (i.e. info from both ears is first combined here)

critical for LOCALIZING

Question 9

Inferior Colliculus

in?

Answer 9

in Tectum of Midbrain

these, like all subsequent sites along pathway are BINAURAL

some from contra-lateral Cochlear Nucleus

Most from ipsi-lateral Superior Olive

INTEGRATES with visual info in Superior Colliculus

helps map source of sight/sound

Question 10

Medial Geniculate Nucleus (MGN)

Answer 10

of Thalamus
includes Tonotopic Map (as do other previous & subsequent sites) -
i.e. Cells that respond to highest frequencies next to cells that respond to medium-high, next to medium, etc.

Question 11

A1

Answer 11

• Primary Projection Area, along Lateral Sulcus of Temporal Cortex
• Tonotopic/Amplitude Map
• Some cells respond best to simple (sine-wave) tones, others to more complex sounds (e.g. “sweeps” that rise or fall in freq)
• Other A1 areas respond per location of sound source (depends on comparing info to two ears – see above)

Question 12

Tonotopic/Amplitude Map

Answer 12

High to low frequency : anterior to posterior; High to low amplitude : lateral to medial

Question 13

A2

damage?

Auditory Agnosia?

Answer 13

• Secondary Auditory Cortex, also in Temporal Lobe
• • Most respond best to complex sounds (familiar noises, speech sounds)
• Damage to A2 not necessarily result in deafness, but Auditory Agnosia = inability to recognize/identify familiar sounds

Question 14

Higher Auditory

Answer 14

– Processes complex patterns;

• Integrates auditory input with other perceptual and cognitive activity
• e.g. Wernicke’s Area for comprehension of speech, esp in left hemisphere
• e.g. Music, esp in right hemisphere

Question 15

Auditory Pathway has much more _______ than Visual

Answer 15

sub-cortical processing

Question 16

Cortical mainly for

Answer 16

complex combos, sequences

Question 17

Unlike visual system, auditory localization is by….

Answer 17

primitive hindbrain (Medulla) for survival: “Orienting Reflex” (HEY!!!)