Audition and vestibular system
Purves et al., Chapters 13 and 14 respetively
(not all of this is in the book)
Intensity dB = 20 log (pressure 1/pressure2)
standard is 0.0002 dynes/cm2
Threshold amplitude of vibration is 10-11 m (10 pm)
Fig. 13.1 p. 278
waves of compressions and rarefactions of air (must have medium) described
by sine wave
Frequency Hz cycles per sec
vibration - 20 - 20,000 Hz, above which is ultrasound .
Audibility curve - Intensity [dB] vs log (freq) [Hz] very sensitive
Fig. 13.3 p. 282
pinna, eardrum=tympanic membrane, ossicles, cochlea, part of nerve VIII
= cochlear nerve
hammer, anvil, stirrup=malleus, incus, stapes - to match impedance of air
oval window is "inner ear drum"
20:1 "amplification" tympanic to oval
cochlea near vestibular apparatus
Fig. 13.4 p. 285
higher magnification, most importantly basilar and tectorial membrane
also inner hair cells (with afferent neurons) and outer hair cells with
possibly outer hair cells do some motor thing to sharpen frequency discrimination
At about 1000 Hz, you can tell the difference of a few Hz. This is explained
by Helmholtz's place theory as modified by lateral inhibition as described
in Bekesy's (1961) Nobel
Prize winning work. You can get the audio oscillator calibrated to be slightly
different from a tuning fork by listening for beats. At low frequencies,
frequency discrimination is better explained by Rutherford's telephone theory.
Here, frequencies to both ears can cause neural impulses that stay true
to the frequency so that beats can be from neural comparison from the two
Two tuning forks that are near but not identical give beats if you listen
to them simultaneously. Beats arise from the constructive and destructive
interference of sound waves at the physical level. There would be one beat
per second if the two tuning forks differed by 1 Hz. Then, if the tuning
forks differ by a few Hz, you can hear the difference in pitch if you listen
to one then another.
For low frequencies:
G. Oster , Auditory Beats in the Brain, Scientific American, Vol 229, October
1973, pp. 94-102
Back to Lecture.
Fig. 13.5 p. 286
Vibration of basilar membrane is mapped by tonotopy
fluid vibration at oval window through helicotrema
released at round window
Frequency discrimination is mapped at high frequencies this way
Frequency discrimination very good - 2 Hz at 1000 Hz
Georg von Bekesy's data pertaining to Helmholtz's place (resonance) theory
1961 Nobel "physical mechanism of stimulation within the coclea"
Fig. 13.11 p. 293
"tuning curves" at different frequencies
for receptor is broad, while for higher order nerves, it is sharp
Lateral inhibition in ascending path sharpens tuning curve
Basilar membrane - high vs low maps to "place" in cochlear nerve
- there is a frequency mapping on the cortex
tonotopy - in A1 = Brodman # 41
Fig. 13.11 p. 293
Frequency discrimination at low frequencies
there was another theory, Rutherford's "telephone" theory
phase-locking gives volley principle up to 4 kHz
Fig. 13.15 p. 298
map of cortex tonotopy
Fig. 13.4 p 285 (again)
Fig. 13.6 p. 287
hair cells on basilar and tectorial membranes
3,500 inner hair cells
many more outer hair cells
Bend as basilar membrane vibrates relative to tectorial membrane
IABelyantseva et al., Myosin-XVa is required for tip localization of whirlin
and differential elongation of hair-cell stereocilia, Nature Cell Biol,
7, 148-156, 2005
Myosin-XVa is product of shaker2 gene
whirlin is product of whirler gene
mutants cause deafness and improper detection of head movement.
Stereocilia need to be different lengths, shaped like a staircase, deficient
Myosin transports whirlin to tips
Fig. 13.7 p. 288
EM. Note kinocilium vs stereocilia (B) and tip links (D)
Fig. 13.8 p 288
Fig. 13.9 p. 289
kinocilium (real cilium, missing in post-natal human hair cells)
plus about 30 stereoocilia
mechanoreception assisted by tip links - depolarization if move toward kinocilium
hyperpolarize if in opposite direction
Threshold displacement is about 0.3 nm, electric potential in 10 micro seconds
SSidi et al., NompC TRP channel required for vertebrate sensory hair cell
mechanotransduction, Science 301, 96-99, 2003.
TRP discussed n somatosensation.
and smell and taste.
NompC=no mechanoreceptor potential (in Drosophila bristles) also
in C. elegans.
In this paper, it is shown that this is a hair cell channel in zebrafish
Fig. 13.10 p. 290
perilymph is fluid of scala vestibuli and scala tympani is like CSF - bathes
baso-lateral hair cell
High K+ in endolymph of scala media (bathing hairs)
stria vascularis (endothelium lining scala media) pumps ions to produce
this unusual extracellular fluid
thus when channels open, K+ comes into cell
endocochlear potential endolymph 80 mV more + than perilymph
Fig. 13.12 p. 294
Very complex- but eye does have synapses in eye (retina), while ear does
Auditory nerve to dorsal and ventral cochlear nucleus - no crossing
Then connect in superior olivary nucleus ipsi- & contra- lateral
whose postsynaptic cells, in turn, go to inf. colliculus
Postsynaptics of inferior colliculus go to Medial Geniculate Body
Medial Geniculate to ipsilateral auditory cortex
Fig. 13.15 p. 298
various parts of auditory cortex
difference in time of arrival and intensity (in big headed animals) [human
700 micro sceond difference]
(speed of sound 1087 ft (331 m) / s in air)
Localization up and down does not rely on 2 ears, may relate to pinna
small-headed animals are extraordinary
Fig. 13.13 p 295
medial superior olivary nucleus important for coincidence detection of time
phase locking important in input - barn owls good at this
Fig. 13.14 p 296
lateral superior olive (and median nucleus of the trapezoid body) calculates
on the basis of intensity difference
bat echolocation biosonar
bat nocturnal, predator, insect "flickers"
moths avoid bats
medial geniculate important
Box A hearing loss p 279
conduction deafness, nerve deafness
also tinnitus - ringing in the ears
lecture is not as detailed as text.
Fig. 14.1 p. 304
utricle and sacculus linear motions
3 semicircular canals - rotations
Fig. 14.3 p. 308
Fig. 14.4 p. 308
stones (otoconia) provide mass for bending in utricle and sacculus
striola divides hair cells with differing polarities
Fig. 14.7 p. 311
Ampulla and cupula displaced as semicircular canal fluid is displaced
Fig. 14.10 p. 313
circuit for eye movements
involving Scarpa's ganglion, vestibular nucleus, abducens (VI) nucleus and
oculomotor (III) nucleus
Box C pp. 314-315
neurology done by irrigating one ear with cold water
Fig. 14.11 p. 318
vestibulo spinal control from vestibular nucleus (integrates with cerebellar
input) to lateral vestibulospinal tract and medial longitudinal fasciculus
Fig. 14.12 p 319
also projection to integrate with somatosensory and muscle spindle senses
Exam questions from 2005 - 2011 relating to this outline
The human audibility curve plots Y as a function of X. Answer either
what is on the Y OR X axes.
ordinate is threshold plotted in intensity, plotted logarythmically, abscissa
is frequency in Hz where log plotting is for convenience
What is the relevance of the value 0.0002 dynes/cm2 in hearing?
that is the denominator, the pressure standard in defining dB
What is the relevance of the value 20,000 Hz in human and animal hearing?
it is the upper limit of frequency for hearing by young people, above that
is ultrasound that dogs and bats can hear
Pressure is passed from the scala vestibuli through the helicotrema (cochlear
apex) to the scala tympani and released at the round window. The pressure
is delivered to the cochlea by (name the third [final] bone OR the "membrane"
[inner ear drum]).
stirrup=stapes, oval window
Cells in the auditory cortex are responsive to a narrow range of frequencies.
By contrast, the tuning curve for a cell in cranial nerve VIII is wider.
Bekesy, the Nobel Prize winner, argued that this was because of what type
A figure was shown to you with hair cells and the axons they are connected
to. On the basis of how that figure was labeled, it was stated that outer
hair cells do not function as receptors. What was it about the axons connected
to outer hair cells that raised this issue?
those axons were called efferent
Tip links assist channels (answer either) (1) for what ion? Or (2) located
on what specific subcellular component?
Regarding the inferior colliculus, answer either (1) It's cells synapse
where? Or (2) It receives input from what nucleus?
auditory cortes, cochlear nucleus and olive
How do insectivorous bats use sound to catch their prey?
In addition to input from vestibular apparatus, the vestibular nuclei that
form the vestibulo-spinal tracts receive input from what major brain location?
The human audibility curve is the threshold for hearing as a function of
frequency. The Y axis could be plotted as intensity in dynes per square
centimeter (plotted logarithmically from 0.0001 to 100) or, alternatively,
what more customary term for intensity (from 0 to 120)?
Answer either: (1) what the tonotopic organization of the primary auditory
cortex looks like; or (2) how would you demonstrate the tonotopic organization
of the primary auditory cortex?
cells that respond to low frequency at one end, high at the other, record
from places and run through a range of stimulus frequencies and see which
frequency each place responds to best
What causes the channels that mediate hearing to open?
mechanosensitive, would be membrane deformation, assisted by tip links
While jogging, you trip and start to fall. Name a sensory organ or a spinal
pathway involved in the elicited responses of your spinal motor neurons.
vestibular apparatus, vestibulospinal tract
Two tuning forks give 5 beats per second if you listen with one ear. Under
what circumstances would you hear beats if you held each near opposite ears?
(Assume you cannot hear either with the ear on the other side.) Alternatively
answer this: What theory does this phenomenon of binaural beats support?
low frequency, Rutherford telephone theory
Imagine that you have come up with a nearly magical technique to record
and graph the responses of an auditory hair cell as a function of frequency.
How would that graph compare with a similar presentation of the tuning curve
of a cell in the primary auditory cortex?
much wider on the frequency axis
Why is it important that auditory receptor cells have voltage-gated calcium
for release of transmitter vesicles
What is the difference between a kinocilium and stereocilia?
kino is real cilium with 9 plus 2, stereocilia are not
Where (if at all) does the auditory input (from one ear) become bilateral?
Otoconia are used Answer either (1) in what structures? Or (2) to stimulate
what kind of cells?
utricle and saccule, hair cells
Information from the vestibular system integrates with information (from
what major brain structure?) for the vestibulospinal tract.
What does the striola divide?
two sides of utricle or saccule with mirror imazge hair cells
A tip link helps in the opening of a channel to what ion?
Bekesy won a Nobel Prize for showing that Helmholtz's place theory was fundamentally
correct but that the localization was much more crude than Helmholtz envisioned.
he rationalize this discrepency to account for very narrow tuning curves
and high resolution localization higher up?
What is unusual about the axons connected to the outer hair cells (in contrast
with those for the inner hair cells)?
they are efferent
The medial lemniscus is part of what system?
What kind of stimulus do bats use to find moths at night?
The cupula and the ampulla are part of what system?
vestibular (semicircular canals)
How do stereocilia differ from the kinocilium structurally?
they lack 9+2 microtubules
For what aspect of hearing is the speed of sound relevant?
A pathway from vestibular nuclei through nuclei for cranial nerves III and
VI is important for what behavior?
eye movement, vestibular ocular reflex
When the audio oscillator and tuning fork are a few Hz apart at about 1000
Hz, what explains beats that you hear with one ear?
constructive and destructive interference of sound waves
Endolymph and perilymph are both extracellular fluid compartments. Why is
there an 80 mV potential where the endolymph is more positive than the perilymph?
because of the high potassium ion concentration in the endolymph
Depolarization of the inner hair cell causes entry of calcium ions. What
effect do these calcium ions have?
release of synaptic transmitter vesicles
What is the difference in localization of vibrations for low vs high frequencies
in the basilar membrane?
low toward helicotrema, higher toward stapes
Neurons of the olive were diagrammed in your book involved in sound localization.
Why are there no such neurons in the spiral ganglion or in the cochlear
they do not have inputs from both ears
Between the inferior colliculus and the auditory cortex is a synapse in
what specific relay station?
medial geniculate of thalamus
Hair cells are located only in a bulge, not throughout the semicircular
canal. What is this bulge called?
ampulla where cupula resides
Name one of the two compartments connected by the helicotrema.
scala vestibuli and scala tympani
Describe the results leading to the conclusion that there is tonotopic organization
of the primary auditory cortex.
rostral part responds to low freq & caudal to high
Mutants of the whirler gene cause improper detection of head orientation.
Why is it no surprise that the animals are also deaf?
affects stereocilia, and hair cells are used in hearing and balance
There is an 80 mV endocochlear potential between the endolymph and the perilymph.
endolymph has high K+, perilymph low
In terms of ions or potential, what causes release of transmitter vesicles
in auditory receptor cells?
influx of K+ causes depolarization causes transmitter release
What is missing in the following list of sites for auditory synapses: (Cochlear
nuclei, nucleus of lateral lemniscus, inferior colliculus, medial geniculate
of the thalamus, and primary auditory cortex)?
What notable control does the vestibular apparatus exert in addition to
descending influences to the ventral horn of the spinal cord and input to
the sensory cortex?
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