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NAB > 4c. The Peripheral Auditory System > Flashcards

4c. The Peripheral Auditory System Flashcards

1
Q

External Auditory Meatus

- Effect on Sound

A

Increases amplitude (dB) of sounds with 2-5kHz frequency, which is the range of frequencies that coincides with human speech

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2
Q

Length of Outer Ear Canal Equation

A

F = c/4L

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3
Q

Middle Ear

- 3 Functions

A
  • Impendance matching between the air and cochlear fluids
  • Protection from loud sounds, especially self-vocalisations
  • Anti-masking of high frequency sounds by low frequency sounds
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4
Q

Impendance Matching

-2 Methods

A
  • Relative areas of tympanic and oval membrane, where the tympanic is much larger
  • Ossicle lever ratio, where the malleus is longer than the incus
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5
Q

Impendance Matching

- Effect

A

30dB increase in sound pressure from airborne sound to oval window

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6
Q

Anti-Masking

A

Antimasking of high frequency sounds by low frequency sounds, particularly at high sound levels, acting as a high-pass filter

Achieved by middle ear muscles

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7
Q

Middle Ear Muscles

- Delay

A

Contract 100ms after sharp loud sounds, so cannot protect from them

Contract before self-made vocalisations

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8
Q

Middle Ear Muscles

- Function

A
  • Attenuate low frequency more than high frequency, acting as a high pass filter
  • Protect from loud sounds and self-vocalisations
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9
Q

Middle Ear Muscles

- 2

A
  • Tensor tympani

- Stapedius

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10
Q

Middle Ear Muscle Reflex

- Activation

A

Sounds 80-90dB above hearing threshold

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11
Q

Middle Ear Muscle Reflex

- Pathway

A
  1. Cochlea

CNVIII

  1. Ventral cochlear nucleus

Trapezoid body

  1. Both superior olivary complexes (brainstem)
  2. Facial nerve nuclei
    - Ipsilateral projects to both
    - Contralateral only to its own

CNVII

  1. Stapedius muscle contraction
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12
Q

Hearing Loss

- 2 Types

A
  • Conductive

- Sensorineural

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13
Q

Sensorineural Hearing Loss

- Definition

A

Cochlea or auditory pathway is damaged

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14
Q

Conductive Hearing Loss

- Definition

A

Pathology that prevents conduction of sound to the cochlea

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15
Q

Conductive Hearing Loss

- Causes

A
  • Otitis
  • Wax build up
  • Tumours
  • Tympanic rupture
  • Nerve defects
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16
Q

Rinne Test

A

Differentiates between conductive and sensorineural hearing loss

Placing a vibrating tuning form on the mastoid process and the entrance of the external auditory meatus.

Sensorineural = air conduction is better than bone conduction

Conductive = bone conduction is better than air conduction

17
Q

Basilar Membrane

- Function

A

Decompose sounds into their component frequencies

18
Q

Auditory Transduction

- Speed

A

Direct mechanical system with no 2nd messenger cascade = fast

19
Q

Basilar Membrane

- Functional Properties

A

Creates a tonotopic map along its length

Thick, wide, stiff base vibrates at high frequencies

Thin, narrow, less stiff base vibrates at low frequencies

20
Q

Auditory Transduction

- Stereocilia Movement

A

Sheering towards the tallest stereo cilia (kinocilium) opens mechanically gated ion channels
- Depolarisation

Sheering away from the tallest stereo cilia (kinocilium) closes mechanically gated ion channels
= Hyperpolarisation

21
Q

Auditory Transduction

- Transducer Current

A

K+ influx

Driving force is:

  • Electrical, due to gradient of 130mV
  • Concentration, as K+ is abundant in endolymph
22
Q

Endolymph Composition

A

Low Na+
Low Ca2+
High K+ maintained by stria vascularis

23
Q

Endocochlear Potential

A

+80mV

24
Q

Perilymph Composition

A

High Na+
Low K+

Similar to CSF

25
Q

Auditory Transduction

- Outer Hair Cells

A

Depolarisation decreases OHC length, feeding back on the basilar membrane augmenting its motion

26
Q

Outer Hair Cells

- 3 Roles

A
  • Increase sensitivity
  • Frequency selectivity through lateral inhibition
  • Oto-acoustic emissions
27
Q

Inner Hair Cells

- 2 Roles

A
  • Decline in phase locking

- Adaptation at the synapse

28
Q

Frequency Resolution

A

The ability to detect 1 frequency in a multifrequency complex stimulus, when all components are presented simultaneously.

Determined at the basilar membrane.

29
Q

Efferent Innervation of the Cochlea

A
  • Lateral pathway

- Medial Pathway

30
Q

Efferent Innervation of the Cochlea

- Lateral Pathway

A

Neurones with their cell body in the lateral olivocochlear nuclei synapse with dendrites of afferent type I ganglion cells that innervate inner hair cells

31
Q

Efferent Innervation of the Cochlea

- Lateral Pathway Role

A

Very little is known about the role of these neurones

32
Q

Efferent Innervation of the Cochlea

- Medial Pathway

A

Neurones with their cell body medial to the lateral olivocochlear nuclei, in the peri-olivary region of the superior olive synapse directly with outer hair cells

33
Q

Efferent Innervation of the Cochlea

- Medial Pathway Roles

A
  • Protection from loud sounds

- Anti-masking

34
Q

Otoacoustic Emissions

A

Sounds generated by the movement of the sensory hair cells in the cochlea

Strongest piece of evidence suggesting that the OHCs are mediating an active process.

35
Q

Otoacoustic Emissions

- Use

A

Measurement is used to diagnose neonatal deafness, in whom it is difficult to establish the absence of hearing.

36
Q

Otoacoustic Emission

- Loss

A

Lost in patients with significant sensorineural hearing loss

37
Q

Prebycusis

- Description

A

Threshold for hearing increases with age.

Hearing at high frequencies also decreases

38
Q

Prebycusis

- Cause

A

Lateral wall degeneration causing loss of endocochlear potential

39
Q

Prebycusis

- Test

A

Selectively lowering the endocochlear potential in 1 ear by application fo furosemide to the round window, causing a loss in threshold which is greater at high frequencies than low frequencies

NAB (37 decks)

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