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Medical Science II: Nervous System > 1.5 The Auditory System > Flashcards

1.5 The Auditory System Flashcards

1
Q

What causes sound

A

disturbance of air molecules that makes up the sound wave consists of zones of compression (pressure increases) and zones of rarefaction (pressure decreases)

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2
Q

what determines the sound waves amplitude

A

the difference between pressure of molecules in zones of compression and rarefactions

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3
Q

Whats the external auditory canal

A

first step in hearing is sound waves entering this (auditory meatus)

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4
Q

what helps amplify and direct sound

A

the shapes of the outer ear (pinna or auricle) and the meatus help to amplify
- continuous vibrations of pressure waves spread down this

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5
Q

what happens as the sound reaches the tympanic membrane (ear drum)

A

it vibrates the same frequency as the sound wave
bows inwards during compression (higher freq)
returns to rest at rarefaction
distance moved depends on the pressure and so measure amplitude

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6
Q

what is the tympanic membrane (ear drum)

A

it is at the end of the meatus

- it is stretched across the canal separating outer and middle ears

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7
Q

what is the middle ear cavity

A

an air filled cavity in the temporal bone of the skull

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8
Q

what is the auditory (Eustachian) tube

A

connects the middle air to pharynx

exposes middle ear cavity to atmospheric air pressure

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9
Q

what is the second step in hearing

A

transmission of sound energy from tympanic membrane through middle ear to inner ear

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10
Q

what is the inner ear called

A

the cochlea

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11
Q

what is the cochlea

A

fluid filled spiral shaped passage in the temporal bone

it is a coiled structure of progressively decreasing diameter

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12
Q

what is in the temporal bone

A

the cochlea and semi-circular canals used in the vestibular system

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13
Q

what do ossicles do

A

as liquid is more difficult to move than air the sound pressure must be amplified which is what it does

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14
Q

what is the structure of ossicles

A 
chain of 3 bones
- malleus
- incus
- stapes
that act a piston and couple the tympanic membrane vibratios to the oval window (effectively impedance matching)
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15
Q

what is the oval window

A

much smaller than the tympanic membrane so force per unit area increases by 15 to 20 time

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16
Q

what is scalae

A

3 liquid-filled compartments

  • scala vestibui
  • scala typmani
  • scala media
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17
Q

what is scala vestibui

A

farthest from the base and has the oval window at the basal end

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18
Q

what is scala typmani

A

at the cochlear base and has the round window as its base

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19
Q

what is the scala media

A

it is within the cochlear duct which separates the 2 chambers

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20
Q

what is the one side of the cochlear formed of

A

by the basilar membrane upon which sits the organ of Corti (contains ear’s receptor cells)

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21
Q

what vibrates the basilar membrane

A

pressure differences across the cochlear duct

22
Q

what is the frequency like at the distal end or apex of basilar membrane

A

membrane is fairly broad and flaccid so more sensitive to low frequency oscillations

23
Q

what is the frequency like at the proximal end (near the tympanum) of basilar membrane

A

membrane is stiffer and more sensitive to high sound frequencies

24
Q

what is the scale of frequencies of basilar membrane against displacement

A

logarithmic

25
what is a tonotopic map
neighbouring values in stimulus space are encoded by neighbouring sensory units facilitates signal processing such as lateral inhibition
26
what is the organ of Corti
receptor organ of the inner ear
27
what does the organ of Corti contain
16,000 hair cells innervated by approx 30,000 afferent nerve fibres which carry info to the brain
28
how are the hair cells in the organ of Corti organised
tonotopically organised at any position along the basilar membrane, the hair cells are most sensitive to a particular frequency and these freq are logarithmically mapped in ascending order from the cochlea's apex to its base
29
what do hair cell mechanoreceptors have
stereocilia (and one kinocilium) protruding from one end - transform pressure waes into receptor potentials - in contact with overhanging tectorial membrane
30
what happens as basilar membrane is displaced
hair cells more relative to the tectorial membrane causing shear of the stereocilia
31
what does shear of the stereocilia cause
opens ion channels that are gated with spring like structures depending on direction, ion channels open for Ca of K other channels contribute to the RP response
32
where is cochlea info sent
to the cochlear nucleus in the medulla conveyed by central processes of cochlear ganglion cells info relayed to different types of neurones in the cortex (tonotopic arrangements maintained)
33
dorsal acoustic stria
pathway oicking up info from the dorsal cochlear nucleus
34
what connects to the inferior colliculus in mid brain
projections run through the pons to connect
35
what happens after inferior colliculus
info passed to medial geniculate nucleus and then to the primary auditory cortex
36
what does the intermediate acoustic stria do
connects the cochlear nucleus with the nucleus of the lateral lemniscus in the pons where the info is sent to the inferior colliculus
37
where does the trapezoid body send info to
the superior olivary nuclei
38
what happens at superior olivary nuclei
first binaural interactions occur which are important in sound localisation
39
where is the second binaural relay station
found in the nucleus of the lateral lemniscus in the pons
40
Afferent nerve fibres from cochlear ganglion cells
bundled in the cochlear or auditory component of the 8th cranial nerve and terminates exclusively in the cochlear nuclei in a tonotopic organisation
41
where do fibres that start at apical end of cochlea end
ventrally in the ventral and dorsal cochlear nuclei
42
where do fibres that start at basal end
terminate dorsally
43
stellate cells
o Encode sound frequency o Each cell responds to a characteristic frequency o Depolarising current injections induce regularly spaced spikes
44
bushy cells
o Single spike upon current injection | o Encode sound onset and horizontal sound localisation
45
fusiform cells
Vertical sound localisation
46
octopus cells
May be involved in recognition of sound patterns
47
whats the spatio-temporal correlation of signals used for
used to extract localisation information in the horizontal plan
48
what happens when Acoustic signal from right ear (ipsilateral input) is sent to a 1D spatial array of interneurons
o These also receive an input from the contralateral ear | o An interneuron generates an output signal if both inputs coincide.
49
Which interneuron fires encodes where the source of the sound is.
o Relies on the fact that electrical signals travel at finite speeds o To obtain simultaneous arrival of a signal elicited by sound first picked up in the left ear, with a signal induced by the same sound source in the right ear, the left ear signals is made to travel along a long “delay line” which compensates for the later arrival of the right ear signal. - Very short membrane time constants, otherwise also nearly coincident inputs would result in their activation.
50
what can cause sensorineural hearing loss
Intense stimulation of the hair cells may cause permanent damage as the stereocilia lose their ability to return to neutral position o This results in sensorineural hearing loss
51
what do cochlear implants do
bypass the hair cells by frequency/positiondependent direct extracellular stimulation of afferent fibres o Requires sound processing and tonotopic arrangement of electrodes

Medical Science II: Nervous System (7 decks)

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