Audition and Central Auditory Pathways Flashcards
What structures are injured to cause deafness?
hair cells
What structures are still intact for deaf people that allow the use of cochlear prostheses?
afferent fibers from hair cells
How do cochlear prosthetics work?
bypass hair cells by implanting multiple electrodes into scala tympani to directly activate different afferent nerve fibers based on the different auditory stimuli
What is an auditory stimulus?
rapid fluctuations in air pressure, rarefaction and compression of air molecules
What is the amplitude of an auditory stimulus?
the magnitude of pressure change
What scale measures the physical magnitude of sound stimuli? How much do you have to increase the sound pressure to compensate for a 40 dB loss of hearing?
decibel, 100x
Where in the auditory system does frequency analysis occur?
basilar membrane in the cochlea
Why is there a 30 dB transmission loss of incident energy at the oval window?
cochlea is fluid filled and it is harder to impart fluid motion than air motion, only 1/1000 of the energy transmits
What does the change in area from 60 mm^2 in the tympanic membrane to 3 mm^2 in the oval window do?
amplifies the pressure transmitted by 20 fold at the oval window (to help compensate for loss of incident energy due to fluid)
Why is the lever action of the ossicular chain important?
increases the pressure felt at the tympanic membrane by 1.3 to help compensate for transmission loss
What is tympanometry? What is measured? What pathology is tested for?
technique to measure impedance of middle ear to sound, measure the amount of sound waves reflected using a mic, tests for conductive hearing loss which presents with more sound waves reflected back
What changes in the basilar membrane as you go from base to apex?
gets wider and gets less stiff
Does deflection increase or decrease as you move towards apex of basilar membrane? What about phase lag?
both increase
What happens when stapes moves into the oval window? when it moves out? what does this create?
when it moves in compresses fluid to create downward bulge in round window, when it moves out creates an upward bulge, together it creates a full traveling wave
What is the envelope?
maximum deflection in the basilar membrane a specific frequency will reach before dissipating quickly
Where do high frequency waves deflect near? low frequency waves?
high frequency closest to base, low frequency closest to apex
Why is the activation of certain receptors correlated to hearing certain frequencies?
because receptors are arranged in an orderly manner along the basilar membrane and the frequency affects the deflection pattern of the basilar membrane to narrowly activate a certain area on the membrane (because of position of max stimulation)
How can you activate a hair cell that is not at the exact area of maximum deflection?
increasing sound intensity since it increases the amplitude of the envelope and can incidentally stimulate hair cells near the point of maximal deflection
How does pushing on the basilar membrane stimulate hair cells?
deflecting basilar membrane shears cilia of hair cells in one direction, affects the permeability of the auditory cell membrane to allow change in current
If cilia shears towards kinocilia, does this depolarize or hyperpolarize the hair cell?
depolarizes
Where are the short and stiff hair cells? Longer and less stiff?
base of basilar membrane, apex of basilar membrane
Are hair cells spontaneously active?
yes
What does mechanical activation does to the spontaneous voltage oscillations of hair cells?
amplifies them because the characteristic frequency of oscillation matches the frequency that is most responsive to mechanical stimuli
What does the central auditory system detect, pure tone or patterns?
patterns
How many divisions of cochlear nuclei are there? do they all receive innervation from CN VIII?
3 (dorsal, posteroventral, anteroventral), yes the full range of frequencies represented in each of the 3 nuclei
Is there tonotopic distribution of frequencies in the nuclei?
yes, high frequency dorsally, low frequency ventrally
Is tonotropy maintained in A1?
yes, high frequency is rostral, low frequency is caudal
As you go perpendicular to the cortex, what kind fields of cells do you see?
more complex fields (may need change in frequency or pattern to be activated, etc)
Is auditory cortex needed for pitch discrimination? What does it do?
No, it analyzes pitch patterns
