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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
Q

what is a tonotopic map

A

neighbouring values in stimulus space are encoded by neighbouring sensory units
facilitates signal processing such as lateral
inhibition

26
Q

what is the organ of Corti

A

receptor organ of the inner ear

27
Q

what does the organ of Corti contain

A

16,000 hair cells innervated by approx 30,000 afferent nerve fibres which carry info to the brain

28
Q

how are the hair cells in the organ of Corti organised

A

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
Q

what do hair cell mechanoreceptors have

A

stereocilia (and one kinocilium) protruding from one end

  • transform pressure waes into receptor potentials
  • in contact with overhanging tectorial membrane
30
Q

what happens as basilar membrane is displaced

A

hair cells more relative to the tectorial membrane causing shear of the stereocilia

31
Q

what does shear of the stereocilia cause

A

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
Q

where is cochlea info sent

A

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
Q

dorsal acoustic stria

A

pathway oicking up info from the dorsal cochlear nucleus

34
Q

what connects to the inferior colliculus in mid brain

A

projections run through the pons to connect

35
Q

what happens after inferior colliculus

A

info passed to medial geniculate nucleus and then to the primary auditory cortex

36
Q

what does the intermediate acoustic stria do

A

connects the cochlear nucleus with the nucleus of the lateral lemniscus in the pons where the info is sent to the inferior colliculus

37
Q

where does the trapezoid body send info to

A

the superior olivary nuclei

38
Q

what happens at superior olivary nuclei

A

first binaural interactions occur which are important in sound localisation

39
Q

where is the second binaural relay station

A

found in the nucleus of the lateral lemniscus in the pons

40
Q

Afferent nerve fibres from cochlear ganglion cells

A

bundled in the cochlear or auditory component of the 8th cranial nerve and terminates exclusively in the cochlear nuclei in a tonotopic organisation

41
Q

where do fibres that start at apical end of cochlea end

A

ventrally in the ventral and dorsal cochlear nuclei

42
Q

where do fibres that start at basal end

A

terminate dorsally

43
Q

stellate cells

A

o Encode sound frequency
o Each cell responds to a characteristic frequency
o Depolarising current injections induce regularly spaced spikes

44
Q

bushy cells

A

o Single spike upon current injection

o Encode sound onset and horizontal sound localisation

45
Q

fusiform cells

A

Vertical sound localisation

46
Q

octopus cells

A

May be involved in recognition of sound patterns

47
Q

whats the spatio-temporal correlation of signals used for

A

used to extract localisation information in the horizontal plan

48
Q

what happens when Acoustic signal from right ear (ipsilateral input) is sent to a 1D spatial array of interneurons

A

o These also receive an input from the contralateral ear

o An interneuron generates an output signal if both inputs coincide.

49
Q

Which interneuron fires encodes where the source of the sound is.

A

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
Q

what can cause sensorineural hearing loss

A

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
Q

what do cochlear implants do

A

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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