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MedST IB: Neurobiology and Human Behaviour (NHB) > 4.0 Auditory System > Flashcards

4.0 Auditory System Flashcards

1
Q

What is the range of frequencies that the ear can respond to?

A

20Hz - 20kHz

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2
Q

What is the intensity of sound measured in?

A

Decibels (usually expressed in log scale)

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3
Q

What is the formula for the amplitude of sound (decibels sound pressure level [dB SPL]) ?

A

dB SPL = 20log₁₀P/P₀

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4
Q

What is the minimal audible sound pressure detectable by normal human ears?

A

20μPa

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5
Q

Define auditory threshold:

A

Sound pressure at which pure tone is just heard

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6
Q

Define pain threshold:

A

Sound pressure at which sound becomes painful

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7
Q

Structures of external ear:

A

1) Pinna<br></br>2) EAM

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8
Q

Structures of middle ear:

A

1) Tympanic membrane<br></br>2) Ossicles<br></br>3) Middle ear cavity (temporal bone)

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9
Q

Structures of inner ear:

A

1) Vestibular apparatus (balance)<br></br>2) Cochlea (hearing)

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10
Q

Function of middle ear?

A

Electrical transformer

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11
Q

How does middle ear match the low impedence in air to the high impedence in cochlear fluid?

A

1) Area of eardrum = 14x times the area of footplate of stapes, therefore the pressure at stapes is 14x the eardrum<br></br>2) Ossicular chain acts a lever

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12
Q

What are the muscles of the middle ear?<br></br>What is their function?

A

1) Tensor tympani (attatches to malleus)<br></br>2) Stapedius (alters angle of stapes at oval window)<br></br><br></br>These two muscles reduce sound transmission (thus offer protection)

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13
Q

At what sound levels do the muscles of the middle ear contract (reflex)?

A

80dB SPL

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14
Q

How many dBs can the muscles of middle ear reduce sensitivity by?

A

30 - 40 dB SPL

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15
Q

What is the purpose of the eustachian tube?

A

Equalizes the pressure in the middle ear with atmosphere

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16
Q

Function of helicotrema?

A

Prevents partition from vibrating at subauditory frequencies. Only allows non damaging sounds

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17
Q

Define tonotropic map:

A

Different sound frequencies are mapped along the partition. This is not linear (logarithmic increments)

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18
Q

What is the travelling wave:

A

Caused by vibration of the partition. The partition executes a travelling wave that moves from base to apex. Each point undergoes a sinusoidal vibration with the amplitude being highest at its characteristic place on the tonotropic map.<br></br><br></br>Phase lag (where more apical points lag behind stapedial ones) = proof that this is not a standing wave

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19
Q

Where is the Organ of Corti?

A

On the basilar membrane along the whole length of the partition

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20
Q

What is the gelatinous mass covering the Organ of Corti?

A

Tectorial membrane

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21
Q

How many rows do outer hair cells have?<br></br>How many rows do inner hair cells have?

A

outer hair cells = 3 longitudinal rows<br></br>inner hair cells = 1

22
Q

What is the type of fluid in the following?<br></br><br></br>1) Scala vestibuli<br></br>2) Scala tympani<br></br>3) Scale media

A

1) Scala vestibuli = perilymph<br></br>2) Scala tympani = perilymph<br></br>3) Scale media = Endolymph (more potassium + 100mV more positive)

23
Q

What secretes endolymph?

A

Stria vascularis

24
Q

How does mechano-electrical transduction occur in the streriocilia?

A

Steriocilia = microvilli<br></br><br></br>Movements of steriocilia are linked to opening and closing of <b>cation channels</b><br></br><br></br>Movement towards longest steriocilia = opening<br></br>Movement towards shortest = closing

25
Q

Inner vs Outer hair cells:

A

“<div><img></img></div>”

26
Q

Define presbycusis

A

Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow older

27
Q

What are the afferent neurons of the cochlea?

A

Bipolar cells<br></br><br></br>(axons run in internal auditory meatus)

28
Q

Where are the cell bodies of the bipolar cells?

A

Spiral ganglion (wraps around modiolus)

29
Q

How much divergence occurs in auditory nerve fibres?

A

Lots<br></br>1 inner hair cell → 20 peripheral axons

30
Q

How is intensity coded in auditory nerve fibres?

A

↑ sound pressure → ↑ firing rate<br></br><br></br>This saturates at 40dB > fibre threshold<br></br>(because fibres have different thresholds, overall range of intensities is 80dB)

31
Q

What is a tuning curve?

A

A curve to show the amplitudes at which a specific frequency can be detected

32
Q

Define characteristic frequency:

A

Each fibre shows a specific frequency at which it is more sensitive

33
Q

Define two tone suppression:

A

When two tones are played at the same time, tone B (lying in specific regions of the tuning curve) will be suppressed to enhance the response to tone A (lying in favourable frequency domain)<br></br><br></br>This is useful at enhancing contrast in the frequency domain

34
Q

Define phase locking:

A

Frequencies < 4kHz<br></br>Timing for APs in CN VIII are synchronized with individual cycles of the stimulus<br></br><br></br>At these frequencies there is dual representation of frequency in the discharge of auditory nerve (place code and periodicity code)

35
Q

Why do frequencies >4Hz not have phase locking?

A

1) Cycles are shorter than refractory period<br></br>2) Receptor potentials are filtered off their periodic components by the time constant of the hair cell membrane

36
Q

Define place code:

A

Each fibre has a narrow frequency range (by virtue of the place they arise from in cochlea)<br></br><br></br>Irrespective of temporal pattern, activation of a fibre signals the presence of a limited range of frequencies<br></br><br></br>At high frequencies, only place code works

37
Q

Define periodicity code:

A

Temporal pattern for the discharge (phase-locking)<br></br>Also encodes frequencies <4kHz

38
Q

What determines pitch of a pure tone?

A

Frequency

39
Q

What is the missing fundamental?

A

When several frequencies are present in a complex sound, but the brain assigns a frequency (not originally present) as the fundamental frequency

40
Q

What are the two efferent pathways from superior olive to cochlea?

A

<b>1) Crossed pathway</b><br></br>From contralateral superior olive<br></br>Ends on <b>Outer hair cells</b><br></br>Function - suppresses responses to lower level background noises to emphasise interesting aspects of a sound<br></br><br></br><b>2) Uncrossed pathway</b><br></br>Ends on afferent terminal CN VIII fibres beneath inner hair cells<br></br>Not been studied much

41
Q

How many axons does the CNVIII have in humans?

A

30,000

42
Q

Brief overview of central auditory pathways:

A

CNVIII → Cochlear nuclei (medulla) → Superior olive → Inferior colliculus → Medial geniculate nucleus → Primary auditory cortex (A1)

43
Q

What are the three cochlear nuclei?

A

Dorsal<br></br>Posteroventral<br></br>Anteroventral

44
Q

Where is the Primary auditory cortex?

A

On superior temporal gyrus

45
Q

Where is Broca’s Area? What is it involved with?

A

Frontal cortex<br></br>Involved with speech production

46
Q

Where is Werinke’s Area? What is it involved with?

A

Temporal cortex<br></br>Speech comprehension

47
Q

Broca’s and Werinke’s Areas are _________ represented in the dominant (_______) hemisphere

A

Broca’s and Werinke’s Areas are unilaterally represented in the dominant (usually Left) hemisphere

48
Q

What two angles are used for sound localisation?

A

<b>1) Angle of Azimuth</b><br></br>- Horizontal plane<br></br>- Can be localised to 1-2°<br></br><br></br><b>2) Angle of Elevation</b><br></br>- Mid-sagittal plane<br></br>- Can be localised to 10°

49
Q

Define cone of confusion:

A

A theoretical problem that can arise in a completely symmetrical being where a sound source in a specific location may generate the same interaural time and intensity differences

50
Q

Regarding sound localisation:<br></br><br></br>What does the medial part of superior olive (MSO) process?<br></br>What does the lateral part of superior olive (LSO) process?

A

MSO - interaural time difference<br></br><br></br>LSO - interaural intensity difference

51
Q

What are co-incidence detectors?

A

Cells in MSO that only fire when EPSPs occur simultaneously from both inputs

MedST IB: Neurobiology and Human Behaviour (NHB) (11 decks)

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