AVS and CANS Review Flashcards
How does the sound reach and move through the outer ear? What function does the outer ear serve?
acoustic energy in air the air reaches the pinna, pinna helps to act as funnel to direct acoustic sounds down ear canal, **have two ears so capturing at two sides and have interaural differences (different intensity or phase), conduit (canal) resonating tube closed at one end that has a resonance that enhances sound at regions important to us for speech (2,00 to 5,000 Hz), canal and pinna also server as protection
How does the sound move through the middle ear and what is the function of the middle ear?
it moves through the ™ vibration and ossicles, stapes footplate pushes mechanical vibration into inner ear (footplate to oval window), IMM - so we don’t lose sound, largest boost is area difference between ™ to footplate (spiked heel effect), buckling, and lever action of ossicles, air to mechanical and mechanical to hydraulic (pushing on fluid), would lose 99.9% almost all of energy without IMM to push the fluid in inner ear.
Explain the receptor potential occurring in an inner hair cell—you should include the synapse to cranial nerve VIII but NOT what then happens in CN VIII (Include how frequency and intensity are encoded by the receptor potential)
traveling wave in cochlea that moves the BM from stapes pushing into oval window finding the best movement, (vibrates best at apex for this 500 Hz example), IHC gets its stereocilia sheared shortest to tallest (tip links fanning open) potassium rushes in (high in endolymph), depolarizes causing the triggering of calcium to rush in from opening of calcium ion channel ,calcium rushing in causes which causes the neurotransmitter to rush to the edge of the cell and dumps out onto the synapse (glutamate)
in inner ear, OHC main function in biological mechanical amplification
grading - magnitude modulated -magnitude depends on stimulus intensity (receptor itself is amplitude modulated or graded (small = small voltage change, larger stimulus = large voltage change and more neurotransmitters dumped)
Explain the action potential traveling along a cranial nerve VIII fiber—you can begin with being stimulated at the synapse from an inner hair cell and end with where the CN VIII fibers enters the CANS to synapse on the nuclei (Include how frequency and intensity are encoded by the CN VIII responses)
cn 8 synapses when neurotransmitter dumped, cn 8 fiber is stimulated enough to start an action potential, ap - voltage gated channel opens to allow for sodium to rush in and depolarize that spot on cn 8, the spot resets itself after absolute and refractory period and the electrical charge is maintained by sodium potassium pump, action potentials move forward to next node etc., process repeats. AP propagates down cn 8, cn 8 enters cns at cerepellopontine angle synapsing on cochlear nuclei (AVCN, PVCN, DCN)
**500 Hz carries intensity info in nerve fiber (rate of firing of ap (all or none - loud vs soft), how many fibers are firing (traveling wave stimulated area of bm), which fibers are firing (not every fiber carries the whole range (soft, medium, loud responders)
How do we encode intensity?
rate of firing of action potentials (they are all or none - loud vs soft), how many fibers are firing (traveling wave stimulates what area of bm), which fibers are firing (not every fiber carries the whole range (soft, medium, and loud responders)
Describe how a tuning curve is measured—choose one method and describe how the tuning curve would be measured and plotted and what it means
3 ways we measure: movement of bm, electrode on a nerve fiber - neural firing (in brainstem or cn 8),
PT using masking in a booth
amplitude is on y axis, x axis is frequency of the sound, plot the point when the firing or position changed (when we cause a change or increase from resting rate in the neural firing for ex)
characteristic frequency (best frequency for that area or fiber) = point
damaged OHCs - broader and more rounded
Describe how a post-stimulus time histogram would be measured and how it is plotted and what it is showing us
method for measuring cell response to a stimulus
take action potentials and graph on PSTH its resting, onset, peak, offset, and envelope
x axis - time (firing over time), y axis - number of ap spikes in some time period
action potentials over time measure how diff types of cells respond differently (cn 8 vs cells in cn etc.) (pattern response of cells)
primary ex (after stim, spikes, reaches plateau for a bit, quickly drops off going to resting rate)
what is referred to as envelope
overall graphed pattern over time
Describe the importance of having a variety of different cell types throughout the CANS with a variety of different PSTH (firing) patterns and capabilities?
need the variety to pick up our rich auditory environment and it gives our brain more information about the pattern of sounds so it isn’t just simple pure tones we are perceiving, we need the variety to understand speech, variety of patterns = variety of cells in each nucleus because they have different responses
Describe why the central auditory pathway is considered to be a redundant system and how this is important and what it means for audiological testing
central auditory nervous system once we get in brainstem at cochlear nucleus, send ipsi and contra fibers and the auditory fibers cross over many commissures throughout cans so there is more than one path for auditory information to get from brainstem up to the cortex
if there is a lesion or damage in an area, neural firing can bypass and get around it to still reach the cortex this helps us hear complex things and hear in noise and suffer an injury and still be able to hear and understand it
audiology - hard to find because redundancy is able to bypass lesion in our testing we need to make the test harder and harder gradually in order to catch the lesion through the redundancy to find where it is at
