Neuro: 2.07 - Auditory System 2 - Central Pathways

Front 1

Where does the auditory nerve (CN VIII) synapse?

Back 1

Ventral and Dorsal Cochlear Nuclei

Front 2

What are the two distinct pathways for auditory stimuli?

Back 2

- System for recognizing sounds
- System for localizing sounds

Front 3

What is the pathway starting at the CN VIII for localizing sounds?

Back 3

Green pathway
- CN VIII --> Ventral Cochlear Nucleus (VCN)
- Superior Olivary Complex (SOC) in pons
- SOC is first place for binaural convergence (L and R fibers each go to L and R SOC)
- SOC projects to Inferior Colliculus (IC) in midbrain
- Medial Geniculate Nucleus (MGN) in thalamus
- Terminate in primary auditory cortex (A1)

Front 4

What is the pathway starting at the CN VIII for recognizing sounds?

Back 4

Orange pathway
- CN VIII --> Dorsal and Ventral Cochlear Nuclei (DCN and VCN)
- Directly to contralateral Inferior Colliculus (IC) in midbrain via Lateral Lemniscus
- Medial Geniculate Nucleus (MGN) in thalamus
- Terminate in primary auditory cortex (A1)

Front 5

Which pathways originate in the Ventral Cochlear Nuclei? Dorsal Cochlear Nuclei?

Back 5

- VCN: localizing (green) and recognizing (orange) sound pathways
- DCN: recognizing (orange) sound pathway

Front 6

Which pathway projects from the cochlear nuclei to the Superior Olivary Complex (SOC)?

Back 6

System for localizing sounds (green)

Front 7

Which pathway has binaural convergence?

Back 7

System for localizing sounds (green)
* Starts at superior olivary complex (SOC)

Front 8

What are the similarities between the system for localizing sounds and system for recognizing sounds?

Back 8

- Both go to Inferior Colliculus
- Then go to Medial Geniculate Nucleus
- Terminate at primary auditory complex (A1)

Front 9

What is the location of the primary auditory cortex (A1)?

Back 9

Superior Temporal Lobe, Heschel's gyrus

Front 10

What higher order cortical area does the primary auditory cortex (A1) project to?

Back 10

In left hemisphere, projects to Wernicke's area

Front 11

How is the cortex for Wernicke's area different on the L and R sides?

Back 11

- Expansion of cortex on L to accommodate Wernicke's area
- R side does not show this same expansion
(found in temporal lobes)

Front 12

What is the function of Wernicke's area?

Back 12

Speech interpretation and recognition

Front 13

How are the topography and laterality of the auditory system used to diagnose site of damage?

Back 13

Limited use because:
- Multiple decussations and commissures in ascending pathways
- Information from each ear ascends upon both sides of the brain
- Duplication of pathways makes it difficult to selectively cut afferents from one ear or from one part of frequency spectrum unless lesion occurs peripherally in cochlear nucleus

Front 14

What makes it difficult to selectively cut afferents from one ear or from one part of the frequency spectrum?

Back 14

- Duplication of pathways
- Unless lesion occurs peripherally in cochlear nucleus

Front 15

How is the topography of the auditory system set up?

Back 15

- Hair cells of cochlea are arranged along basilar membrane
- Hair cells at successive positions to be most sensitive to successively lower pitched tones
- High freq. at base of basilar membrane
- Low freq. at apex of basilar membrane

Front 16

What is the receptive field of an auditory nerve cell?

Back 16

Region of the basilar membrane to which it is responsive

Front 17

What is a placecode?

Back 17

Place along basilar membrane that represents a certain pitch (frequency)

Front 18

What is a characteristic frequency?

Back 18

The best frequency that a cell responds to

Front 19

What does a frequency tuning curve describe?

Back 19

How well a cell responds to higher and lower frequencies

Front 20

How does sound intensity affect the frequency tuning curve?

Back 20

Broadens it

Front 21

Where are there tonotopic maps?

Back 21

- Most auditory nuclei (e.g., inferior colliculus (ICC))
- Primary and secondary auditory cortex (A1 and A1)

Front 22

What are the two major functions of the central processing of auditory information?

Back 22

- Recognize the sounds (what is it?)
- Localize the sounds (where is it?)

Front 23

What is the function of Broca's area?

Back 23

Speech production

Front 24

How do lesions of the auditory cortex affect sound sensation?

Back 24

- Does not affect sensation of simple sounds
- Disrupts perception of complex sounds like speech

Front 25

What is "aphasia"?

Back 25

Absence of speech but really is a disturbance of higher complex functions by which meanings are comprehended and expressed

Front 26

How do the cells in the auditory cortex respond differently than the cells at earlier stages of processing?

Back 26

- Cells in the auditory cortex can be selectively responsive to complex features of sounds
- Some cells select for speech components (initial formant and a sustained tone)
- Some cells respond to certain combinations of tones (shown in image)

Front 27

What is a speech sound composed of?

Back 27

- Initial formant that changes over time
- Sustained tone
- E.g., "ka", "ta", and "pa"
- Only differ in the beginning, dynamic component

Front 28

What factors contribute to the ability to localize a sound source?

Back 28

- Extra distance produces a time delay for sound to reach far ear (binaural time)
- Shadowing by head produces an intensity loss (intensity)

Front 29

What structure is specialized to detect auditory time and intensity differences?

Back 29

Superior Olivary Complex (SOC)

Front 30

How do neurons in the superior olivary complex convert a binaural time difference to a place code for location?

Back 30

The neuron will only fire if it has simultaneous input
- Requires a "temporal coincidence"