Auditory Pathway Flashcards
Inner Hair Cells
Connectivity?
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
Auditory Pathway
starts with two types of Hair cells in the Cochlea:
inner hair cells and outer hair cells
Outer Hair Cells
Connectivity?
- 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
Spiral Ganglions
axons of which form Auditory Nerve
also called Auditory Nerve Fibers
NOTE: no ______ in Cochlea, but can get ______ from downstream Superior Olive
Lateral Inhibition
Negative Feedback (Inhibition)
Cochlear Nucleus
in Medulla
Monaural site (left Cochlear Nucleus receives from left ear only, right from right only)
Each Spiral Ganglion has up to…
…. 5 branches that synapse onto different Cochlear Nucleus cells
begin sub-pathways for different information
sequence of Action Potentials from a single Spiral Ganglion might be:
3
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)
Superior Olive
in?
critical for?
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
Inferior Colliculus
in?
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
Medial Geniculate Nucleus (MGN)
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.
A1
- 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)
Tonotopic/Amplitude Map
High to low frequency : anterior to posterior; High to low amplitude : lateral to medial
A2
damage?
Auditory Agnosia?
- 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
Higher Auditory
– 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
