audition (25) Flashcards
in simplistic terms, how do cochlear prosthetics work?
they bypass the hair cells & excite the appropriate nerve fibers
what does the auditory system respond to?
a series of rapid fluctuations in pressure brought about by the rarefaction & compression of air molecules
what does the maximum of the sine wave (in a pressure as a function of time plot) correspond to?
the greatest density or pressure
what does the amplitude in a pressure as a function of time plot represent?
the magnitude of the pressure change
what does the “decibel” compare?
it comes the physical magnitude of any given sound to a standard physical magnitude
how is the standard physical magnitude chosen?
it is one near the normal human threshold for tones to which humans are most sensitive
at the oval window, how much of the incident energy is actually transmitted
only 1/1000
to compensate for the loss of energy at the oval window, how big of an increase is there in pressure?
32 fold increase in pressure
**some confusion on this in the notes, listing different values for increase in pressure.. holler if you understand this
what are some pathologies that could result in conductive losses?
otitis media (middle ear infection), otosclerosis (fixation of the middle ear ossibles) and ear wax buildup in the external ear canal
what is tympanometry?
clinical technique that measures the impedance of the middle ear to sound
what is the membrane in the cochlea called?
the basilar membrane
what does the analysis of the frequency of sound depend on?
on the way the sound waves affects the basilar membrane
as you travel from base to apex on the basilar membrane, what happens to its width and stiffness?
increases in width and decreases in stiffness
for equally applied forces along the membrane, will regions of higher or lower stiffness will be displaced to a greater degree?
regions of lower stiffness
what does a decrease in stiffness from the base to the apex result in?
a increase in phase lag
what does the distance of a traveling wave depend on?
depends upon the frequency of the sound wave producing that traveling wave
how is the traveling wave produced?
- As the stapes moves into the oval window a volume of the scala vestibuli is compressed
- The downward bulge initially occurs near the applied pressure at the base
- The stiff base provides a restoring force that brings the membrane back to a neutral position
- this requires that the volume of compressed fluid is taken up elsewhere & shunted farther along the membrane to a less stiff region on and so
- whem the stapes moves out, an upward bulge is produced which, following the downward bulge produces a full traveling wave
in regards to distance traveled, what does a greater frequency of a sound wave correspond with?
less distance traveled along the basilar membrane
how are auditory receptor cells stimulated?
they are MECHANICALLY stimulated by the displacements of the traveling wave
what are 2 ways to increase the excitation of any auditory nerve fiber?
- by presenting a sound wave frequency with a peak traveling wave displacement nearer the position of that fiber’s receptor cell
- within limits, you can increase the intensity of the sound wave
which structure houses the auditory receptors?
the organ of corti
where is the organ of corti located?
it rests upon the basilar membrane
what is the potential difference between the scala media and the ground?
+80 mV
what is the potential difference across the reticular lamina?
150 mV
what does the shearing action of a wave do to a cilia?
it alters its permeability (the resistance) of the auditory cell membrane allowing for a change in current flow
what does the magnitude of the shearing force depend on?
depends upon the magnitude of the basilar membrane displacement
how do hair cells at different points along the basilar membrane differ from one another?
in the electromechanical properties
what are the properties of the hair cells and their cilia at the base of the cochlea?
narrow & stiff
what is the role of the central auditory system
interpret the discharge patterns of the auditory nerve fibers in order to produce the perception of sound
what are the 3 divisions of the cochlear nuclei?
- dorsal
- posteroventral
- anteroventral
where in the nuclei are high frequencies represented?
dorsally in each of the nuclei
where is the nuclei are low frequencies represented?
ventrally in each of the nuclei
where is the primary auditory cortex?
it occupies the transverse temporal gyrus and is largely buried in the sylvian fissure
how are neurons arranged in area A1?
-Neurons of similar best frequency are arrayed in a strip or belt like structure that runs perpendicular (aligned dorsoventrally for A1) to the high to low frequency tonotopic axis
true or false?
the auditory cortex is involved in pitch itself rather than patterns of pitch
FALSE
the auditory cortex is involved in PATTERNS of pitch
what were the conclusions for the training paradigm for cat discrimination experiment?
- that the auditory cortex does not seem necessary for pitch discrimination
- auditory cortex is move involved with the analysis of pitch patterns than pitch itself
