central auditory system Flashcards
be able to label central pathway diagram!
What are the order of fibers in the auditory system
auditory nerve (first order or primary fibers)
cochlear nucleus (second order fibers)
beyond the cochlear nucleus (main tracts or pathways are represented binaurally)
What percentage of fibers cross over to the contralateral pathway and what stay up the ipsilateral pathway
80% cross over
20% stay the same
Is tonotopic organization maintained throughout the central auditory pathways (even at the auditory cortex)?
yes
The superior olivary complex is the first place with what
binaural representation of sound (combining info from both ears)
believed to be the first stage of binaural processing
What is the SOC important for
giving us perceptual information about localization of sounds in our environment
What are the two regions of the SOC
LSO: lateral superior olive
MSO: medial superior olive
What kind of cells does the LSO have and what its purpose
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
What kind of cells does the MSO have and what is its purpose
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!)
What are two strategies to localize the horizontal position of sound sources, depending on the frequency
Frequencies above 3000 Hz use interaural intensity differences (LSO and MNTB)
Frequencies below 3000 Hz use interaural time differences (MSO)
What is the dominant animal for LSO
small headed animals
what is the dominant animal for MSO
larger heads (frequencies in the MSO wrap around the head)
What are the two reflexes the superior olive mediates
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
When does the stapedius muscle contract
in the presence of loud sounds
prior to and during vocalization
during mastication
randomly and voluntarily
What happens when the stapedius muscle contracts
it causes the middle ear to stiffen and low frequencies are attenuated (mostly frequencies below 1000 Hz)
What are the three theories for why the middle ear muscle exists and which one is the best
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
What kind of alarm contains low and high frequencies
broadband noise alarm
What is the standard alarm
tonal and has its frequencies near 12000 Hz
What is the possible role of the inferior colliculus
to combine information from different processes that occur in the lower brainstem
also responsible for the startle reflex
What is Moro’s response/reflex and what does an absence/presence mean
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
Where is the auditory cortex located
sylvian fissure
What is the physiology of the auditory cortex
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
What is the McGurk Effect
perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception
ba –> ga –> da
What other parts of the brain are involved in music perception
basal ganglia, Broca’s area, VTA, and nucleus accumbens
