central auditory system

Question 1

be able to label central pathway diagram!

Question 2

What are the order of fibers in the auditory system

Answer 2

auditory nerve (first order or primary fibers)

cochlear nucleus (second order fibers)

beyond the cochlear nucleus (main tracts or pathways are represented binaurally)

Question 3

What percentage of fibers cross over to the contralateral pathway and what stay up the ipsilateral pathway

Answer 3

80% cross over
20% stay the same

Question 4

Is tonotopic organization maintained throughout the central auditory pathways (even at the auditory cortex)?

Answer 4

yes

Question 5

The superior olivary complex is the first place with what

Answer 5

binaural representation of sound (combining info from both ears)

believed to be the first stage of binaural processing

Question 6

What is the SOC important for

Answer 6

giving us perceptual information about localization of sounds in our environment

Question 7

What are the two regions of the SOC

Answer 7

LSO: lateral superior olive
MSO: medial superior olive

Question 8

What kind of cells does the LSO have and what its purpose

Answer 8

Excitatory Inhibitory cells (EI)
- ipsilateral are excitatory
- contralateral are inhibitory

cells are likely in charge of coding level (dB) differences between ears

level differences and high frequencies specific to LOS
- inter aural level differences

Question 9

What kind of cells does the MSO have and what is its purpose

Answer 9

excitatory excitatory cells (EE)
- sensitive to stimulation from both ears

cells likely code phase differences between ears

sensitive to inter aural time delays (not frequency!)

Question 10

What are two strategies to localize the horizontal position of sound sources, depending on the frequency

Answer 10

Frequencies above 3000 Hz use interaural intensity differences (LSO and MNTB)

Frequencies below 3000 Hz use interaural time differences (MSO)

Question 11

What is the dominant animal for LSO

Answer 11

small headed animals

Question 12

what is the dominant animal for MSO

Answer 12

larger heads (frequencies in the MSO wrap around the head)

Question 13

What are the two reflexes the superior olive mediates

Answer 13

blink reflex
- eye blink in response to an intern sound (not the startle reflex)

acoustic reflex
- contraction of the stapedius muscle in response to an intense sound
- contracts bilaterally and pulls the stapedius perpendicular to its primary rotary axis

Question 14

When does the stapedius muscle contract

Answer 14

in the presence of loud sounds
prior to and during vocalization
during mastication
randomly and voluntarily

Question 15

What happens when the stapedius muscle contracts

Answer 15

it causes the middle ear to stiffen and low frequencies are attenuated (mostly frequencies below 1000 Hz)

Question 16

What are the three theories for why the middle ear muscle exists and which one is the best

Answer 16

Intensity control (protection from loud sounds)

ossicular chain fixation

perceptual theory *(the best)
- *explains that the purpose of the reflex is to reduce physiological noise
- help animal assess whether a sound exists/originated inside or outside the body

Question 17

What kind of alarm contains low and high frequencies

Answer 17

broadband noise alarm

Question 18

What is the standard alarm

Answer 18

tonal and has its frequencies near 12000 Hz

Question 19

What is the possible role of the inferior colliculus

Answer 19

to combine information from different processes that occur in the lower brainstem

also responsible for the startle reflex

Question 20

What is Moro’s response/reflex and what does an absence/presence mean

Answer 20

response of an infant when allowed to drop a short distance through the air when startled by a sudden intense sound

absence/one-side reflex = broken collar bone or spinal damage

presence = healthy nervous system

Question 21

Where is the auditory cortex located

Answer 21

sylvian fissure

Question 22

What is the physiology of the auditory cortex

Answer 22

tonotopic organization
some cells only respond to complex sounds or to tones that change frequency
some cells are broadly tuned, others are narrowly tuned
phase locking not seen for tones above about 300 Hz
many inhibitory cells
frequency to place mapping is maintained all the way through the auditory system

Question 23

What is the McGurk Effect

Answer 23

perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception

ba –> ga –> da

Question 24

What other parts of the brain are involved in music perception

Answer 24

basal ganglia, Broca’s area, VTA, and nucleus accumbens