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Neuro > Neuro 10: Sound conduction and transduction > Flashcards

Neuro 10: Sound conduction and transduction Flashcards

1
Q

Define sound,

A

Sound = pressure wave in air

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2
Q

Define frequency

A

cycles/ sec (Hz), perceived as pitch

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3
Q

Amplitude

A

intensity, perceived as loudness

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4
Q

Decibel range

A

log scale of loudness (i.e. amplitude)

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5
Q

What structures include the outer ear

A

Pinna (auricle) + external auditory meatus

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6
Q

Function of the outer ear

A

Collects and conducts sound waves towards tympanic membrane

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7
Q

What are the boundaries of the middle ear

A

Air-filled chamber in bone, lying between tympanic membrane laterally, and oval and round windows medially

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8
Q

What structures are in the inner ear

A

Cochlea + organs of balance

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9
Q

Function of the inner ear

A

Hair cells transduce mechanical energy of sound into electrical signal in cochlear nerve

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10
Q

What is contained within the air space in the middle ear

A

The 3 bones of the ear: the maleus, incus and stapes

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11
Q

Which structure contiues on from the tympanic cavity (i.e middle ear)

A

The eustachian tube which links to the nasal cavity (=AUDITORY TUBE)

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12
Q

What is the function of the middle ear (and ear in general)

A

AMPLIFY the sound (conduction through middle ear amplifies sound by 30dB)

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13
Q

How is amplification achieved

A

lever system of articulated ossicles and ratio of area of tympanic membrane to oval window

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14
Q

Protective mechanism

A
  1. Reflex contraction of tensor tympani and stapedius muscles reduces amplitude of vibrations passing through ossicles.. these muscles stabilise the tympanic membrane and the stapes respectively
  2. Auditory tube allows equilibration of air pressure on either side of tympanic membrane
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15
Q

Define conductive hearing loss

A

Sound prevented from reaching cochlea

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16
Q

5 types of conductive hearing loss

A
  • wax
  • otitis media
  • otosclerosis of ossicles -perforated tympanic membrane
  • congenital malformations
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17
Q

When rolled out, what is the top compartment of the chochlea called

A

scala vestibuli

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18
Q

When rolled out, what is the middle compartment of the chochlea called

A

Scala media (bound by membrane)

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19
Q

When rolled out, what is the lower compartment of the chochlea called

A

scala tympani

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20
Q

State which fluid is present in the scala vestibuli, scala media and scala tympani

A

vestibuli and tympani is perilymph, media is endolymph

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21
Q

Whcih membrane separates the scala vestibuli and scala media

A

vestibular (=Reissner’s) membrane

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22
Q

Whcih membrane separates the scala tympani and scala media

A

basilar membrane

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23
Q

Where does the stapes bone articulate to the cochlea

A

at the oval window (it pushes it in and out, which sends vibration through the scala vestibuli then the scala tympani, so the round window pops out)

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24
Q

What is the round window

A

The area of cochlea which can pop out when stapes pushes in.. is is the fluid in scala tympani pushing out into the round window (see video)

25
Q

Where are cochlear hair cells attached to

A

BASILAR MEMBRANE

26
Q

What comprises the organ of corti

A

Hair cells
Tectorial membrane (which overlies the hair cells… hair cells lie between tectorial membrane and basillar membrane)
Spiral ganglion
Stria vascularis

27
Q

Where is the spiral ganglion located

A

ebedded int he modiolus….. innervates hair cells

28
Q

Function of stria vascularis

A

secretes endolymph

29
Q

Chemical properties of endolymph

A

secretes endolymph (high in K+, low in Na+)

30
Q

What is the ultrastructural property of the hair cell

A

Have many stereocilia per cell

31
Q

State 2 types of hair cell

A

inner hair cell – about 3,500 cells arranged in single row, densely innervated by about 10 sensory axons/cell

outer hair cell – about 20,000 cells arranged in 3 rows sparsely innervated: one axon inervates several cells

32
Q

Which hair cell provides information to the brain

A

Inner hair cells

33
Q

Role of outer cells

A

Efferent nerve causes cell to change shape, which in turn amplifies the response to sound of adjacent inner hair cells at the centre of the vibration… ELECTROMOTILITY (mechanical response which drives oscillations in the cell’s length, which occur at the frequency of the incoming sound and provide mechanical feedback amplification)

34
Q

TRANSDUCTION:

what does the basilar membrane do in response to sound

A

Vibrates

35
Q

TRANSDUCTION:

what happens in upward movement of the basilar membrane

A

Upward movement displaces stereocilia away from modiolus → K+ channels open → K+ enters from endolymph → hair cell depolarises

36
Q

TRANSDUCTION:

what happens in downward movement of the basilar membrane

A

Downward movement displaces stereocilia towards modiolus → K+ channels close → hair cell hyperpolarises

37
Q

Why is stria vascularis important in sound transduction

A

Because movement of K+ into cell depends on maintenance of endolymph at +80 mV by stria vascularis

38
Q

TRANSDUCTION: Effect of depolarisation in the body of the hair cell

A

Opens Ca++ channels in body of hair cell

39
Q

TRANSDUCTION How is a nerve activated attached to the inner hair cell

A

Depolarisation leads to Ca2+ release inside cell, this causes glutamate to be released from base –> depolarises axon of spiral ganglion cell → action potential

40
Q

Where in the chochlear are different frequencies picked up

A

Basilar membrane acts as frequency analyser

High frequencies vibrate basilar membrane nearer to base

Low frequencies vibrate membrane nearer to apex

TONOTOPIC ORGANISATION

41
Q

At what range can humans hear

A

20 Hz – 20 kHz

most sensitive 1-3 kHz

42
Q

Define tonotopy

A

spatial organisation of response to frequency is preserved throughout pathway

43
Q

Outline the auditory pathway from cochlea to cortex

A

Spiral ganglion –>

ipsilateral ventral and dorsal cochlear nucleus (still tonotopic organisation in this nucleus) –>

From cochlear nucleus, fibres project to ipsilateral AND contralteral superior olivary nuclei –>

So then from superior olive to inferior colliculus (now containing mix from both ears… still inbrainstem –>

To medial geniculate body in the thalamus –>

Auditory cortex in the cerebral hemisphere

http://pages.ucsd.edu/~johnson/COGS17/17Mnemonics.html

44
Q

Where else do fibres project apart from this central pathway

A

Collateral pathways to reticular formation and cerebellum

45
Q

Function of lateral inhibition in the ascending pathway

A

ascending pathway enhances resolution of similar frequencies

46
Q

Function of inferior colliculi

A

reflexes eg. startle, head turn

47
Q

T/F.. there is no descending pathway in the auditory pathway

A

FDescending pathways provide feedback at all levels

48
Q

How is primary auditory cortex organised

A

subdivided according to frequency response

49
Q

What do cells in the PAC respond to

A

pecific features of sound e.g. on/off, duration, repetition, intensity + some more complex sound patterns e.g. rising/falling frequencies, animal vocalisations

50
Q

Function of secondary cortex

A

Secondary cortex – neurones respond to more complex sound patterns

51
Q

Causes of sensorineural deafness (sensory)

A 
presbyacusis
Exposure to loud noise
Ménière’s disease
Toxicity e.g. some antibiotics
Hereditary disorders
52
Q

Causes of sensorineural deafness (neural)

A

Acoustic neuroma

Viral infection

53
Q

Causes of sensorineural deafness (central)

A

Demyelination in MS

Injury to central auditory pathway (unlikely to cause serious deafness unless both auditory cortices affected)

54
Q

What is the auditory reflex

A

involuntary muscle contraction that occurs in the middle ear in response to high-intensity sound stimuli or when the person starts to vocalize.

The stapedius and tensor tympani muscles of the ossicles contract.[1] The stapedius stiffens the ossicular chain by pulling the stapes (stirrup) of the middle ear away from the oval window of the cochlea and the tensor tympani muscle stiffens the ossicular chain by loading the tympanic membrane when it pulls the malleus (hammer) in toward the middle ear.

Stapedius=facial
tensor tympani= V3

55
Q

What is sound intensity and how is that measured

A

the power carried by sound waves per unit area

(joules/m2)

Decibel scale is used, which is a log scale of loudness

56
Q

What is the impedance

A

The reluctance of a system to receive energy from a source. Ossicles have to match the impedance of the sound wave and reduce energy loss when transferring the sound from the ear bones to the cochlea.

57
Q

Outline the impedance of the cochlea

A

The impedance of the basilar membrane varies along its length, meaning that so does the local resonant frequency

58
Q

What is the resonant frequency

A

The frequency at which the
impedance of the system is
minimal is called the
resonant frequency.

59
Q

What is mechanotransduction

A

This is referring to the point at whch vibrations cause deflection of the hair cells against the tectorial membrane, leading to depolarisation (if the cells are deflected AWAY from the modiolus, leading to K+ influx)

Neuro (16 decks)

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