Auditory System 2: Central Pathways

Question 1

Auditory nerve fibers synapse in the _________

Answer 1

cochlear nucleus

Question 2

Two distinct pathways:

Answer 2

1. Recognition of sound patterns:
   
   • Dorsal and Ventral cochlear nuclei project directly to contralateral inferior colliculus via the lateral lemniscus
2. Localizing sounds:
   
   • Ventral cochlear nucleus also projects to the superior olivary complex (SOC) in the pons
   • SOC: 1st place for binaural convergence
   • Subsequently the SOC projects to inferior colliculus

Question 3

Inferior colliculus relays both pathways to:

Answer 3

• medial geniculate nucleus of the thalamus
  
  • Note: organization is different from visual system where tectum and geniculate nuclei are separate parallel pathways

Question 4

Medial geniculate fibers terminate in:

Answer 4

• primary auditory cortex (A-I, area 41)
  
  • Located in superior temporal lobe, Heschel’s gyrus

Question 5

Where does the primary auditory cortex project?

Answer 5

• Left hemisphere of humans
  
  • Wernicke’s area – speech interpretation
  • Note expansion of cortex on the left.
• Auditory cortex may be hierarchically organized like visual and somatosensory cortex

Question 6

Desribe the arrangement of hair cells:

Answer 6

• Hair cells of cochlea are arranged along the basilar membrane
• Causes hair cells at successive positions to be most sensitive to successively lower pitched tones
• High frequencies represented at the base (narrow end)
• Low frequencies at apical
  end (wide)

Question 7

Receptive field:

Answer 7

• region of the basilar membrane
  to which the auditory cell responsive
• best frequency = characteristic frequency
• Frequency tuning curve: describes
  how well a cell responds to higher
  and lower frequencies
• Increasing sound intensity ⇒ tuning curve broadens

Question 8

Orderly arrangement of tone (frequency) sensitivity is then preserved in the __________ of fibers and cells within each pathway.

Answer 8

relative positions

Question 9

1. Wiernicke’s area is important for _________.
2. Broca’s area is important for _________.

Answer 9

1. speech analysis
2. speech production

Question 10

What would be affected if there were a lesion of the auditory cortex?

Answer 10

• DO NOT AFFECT sensation of simple
  sounds
• DISRUPT perception of complex sounds
  
  • speech
• Wernicke’s aphasia
  
  • Aphasia = absence of speech
  • a disturbance of higher complex functions by which meanings are comprehended and expressed

Question 11

CELLS IN AUDITORY CORTEX CAN BE
SELECTIVELY __________ TO COMPLEX
FEATURES OF SOUNDS

Answer 11

RESPONSIVE

Question 12

Selectivity:

Cells in higher cortical areas

Answer 12

• Selectively responsive to combinations of tones
  
  • speech sounds

Question 13

How is sound located?

Answer 13

Binaural time and intensity differences in the two ears

Question 14

What detects the audtiory time and intensity differences?

Answer 14

• superior olivary complex
• “Temporal coincidence” circuitry in the
  superior olive can create a neural code for
  location in space