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Neurology > Physiology of hearing and vestibular systems > Flashcards

Physiology of hearing and vestibular systems Flashcards

1
Q

What is the function of the Pinna?

A

Catches sound waves and relays them into the eardrum

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2
Q

What are sound molecules?

A

Disturbances of air molecules set up by vibrations in air

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3
Q

Where do the sound waves travel after the pinna?

A

The auditory canal to the tympanic membrane

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4
Q

What are the three bones of the middle ear?

A
  • Malleus (hammer)
  • Incus (anvil)
  • Stapes (stirrup)
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5
Q

What are the muscles of the middle ear?

A
  • Tensor timpani

- Stapedius

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6
Q

What are the three functions of the middle ear?

A
  • damning
  • amplification
  • impedance matching
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7
Q

What are the three parts of the ear?

A

Outer, middle and inner ear

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8
Q

What are the parts of the outer ear?

A

Pinna, auditory canal and tympanic membrane

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9
Q

What are the parts of the inner ear?

A
  • Cochlea (hearing)

- Vestibule and semicircular canal (balance)

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10
Q

How does the tympanic membrane perform its damping functions?

A
  • tympanic membrane is a resonator so it vibrates at the same frequency as the sound waves on its surface
  • its attachment to Malleus, Incus and Stapes also allows it to be a critically dampening
  • reflex to protect the inner ear where get contraction of muscles attached to ossicles which is triggered before you speak but is often too slow for rapid onset loud noises
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11
Q

How does the tympanic membrane perform its amplification functions?

A
  • sound pressure which reaches oval window is increased by:
    1) the lever action
    2) area of tympanic membrane is far greater than oval window
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12
Q

How does the tympanic membrane perform its impedance matching functions?

A

Amplification allows for the same vibration frequency to be produced in liquid even though it is harder to vibrate liquid

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13
Q

What are the three chambers of the cochlear?

A

Scala vestibuli - rich in Na+
scala Tympani - rich in Na+
Scala media - rich in K+

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14
Q

What is the vascular layer of cochlea called?

A

stria vascularis

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15
Q

Describe the nerves in the cochlea

A

spiral ganglion leads to cochlear nerves which lead to temporal cortex of the brain

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16
Q

What is the function of the cochlea?

A

Transforms mechanical deformations into electrical signals

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17
Q

How are mechanical deformations transformed into electrical nerve signals?

A
  • vibrations of oval window compress the fluid of inner ear and set up vibrations in basilar membrane
  • which are then absorbed by deformations of flexible round window
  • basilar membrane contains inner and outer hair cells which set up electrical signals
  • vertical vibrations of basilar membrane are converted to lateral motion of hair cells
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18
Q

Which two cochlear chambers are continuous?

A

scala vestibuli and scala tympani

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19
Q

Which hairs are more important for which function?

A

afferent fibres go to inner hair cells (main transducers)

efferent fibres go to outer hair cells (modulators of sensitivity of inner hair cell)

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20
Q

How do each hair cell create electrical signals?

A
  • hair cells are linked laterally
  • between hair cells are ion channels which can be pulled open
  • allowing potassium to enter hair cell and depolarise cell
  • setting up AP in VIII nerve
  • K+ is allowed back into endolymph via stria vascularis
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21
Q

What are the two characteristics of sound waves?

A 
sound frequency (pitch)
Sound amplitude (volume)
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22
Q

What units do we measure sound in?

A

Decibel

23
Q

What is the calculation of decibels?

A

1 dB = 10 x Log10 actual sound intensity / reference sound intensity

24
Q

How does the cochlea code for frequency differences?

A
  • different frequencies will cause different hair cells along the basilar membrane to be maximally stimulated
  • High frequency will maximally stimulate at oval window
  • Low frequency will maximally stimulate near helicotrema
25
Q

How is amplitude coded for?

A

frequency of the AP of hair cells

26
Q

Why must decibels be a logarithmic scale?

A
  • each 10 db means a sound is twice as loud
27
Q

How can directionality of sound be detected?

A
  • above 3000 Hz can tell which ear the amplitude is greater

- below 3000 Hz can tell by the delay in sound to one ear

28
Q

Where is the auditory cortex of the brain located?

A
  • superior portion of temporal lobe

- within sylvian fissure

29
Q

Describe the structure of the auditory cortex?

A
  • high and low freq sounds registered at different ends
  • topographical map of basilar membrane (each column repeated several times for different locations of sound)
  • association areas are close to the cortex
30
Q

What are the association areas of the auditory cortex?

A
  • Wernickes area (comprehension of speech)

- de Brocas area (production of speech)

31
Q

What symptoms would damage to wernickes area have?

A
  • speak jargon

- wernickes aphasia

32
Q

What happens with damage to de Brocas area?

A

patient knows what they want to say they just can’t get it out

33
Q

What are the different types of deafness?

A
  • Conductive

- Sensorineural

34
Q

What is conductive deafness?

A

impaired sound conduction from pinna to the inner ear

35
Q

What causes conductive deafness?

A
  • Ear wax
  • perforated eardrum
  • fluid in middle ear from infection
  • damaged ossicles
36
Q

What is sensorineural deafness?

A

damage to the hair cells or neural pathways

37
Q

What causes sensorineural deafness?

A
  • loud sounds cause hair cells to be sheared and cant be regenerated
  • basilar membrane can rip with loud sounds
  • antibiotics can enter hair cell channels and disrupt their function and cause degeneration
  • tumours in auditory nerves and vascular damage to medulla
38
Q

How can audiometry distinguish between types of deafness?

A
  • detects thresholds for hearing at different frequencies

- nerve deafness results in defects at higher frequency reception

39
Q

What body processes require input from the vestibular system (balance)

A
  • many reflexes
  • many eye movements
  • setting background posture against which we move
  • progress of movement at any given time
40
Q

Which parts of the inner ear are used in balance?

A

semi-circular canals (3 canals on each side) and vestibules (utricle and saccule)
- all detect acceleration

41
Q

Describe the structure of the semicircular canals

A
  • base of semicircular canal swelling called ampulla
  • ampulla contains cristae ampullaris (gelatinous ridge)
  • cupula is gelatinous mass extending from ridge containing processes of hair cell
  • hair cells contain motile cilia and one non-motile cilia called kinocilium
42
Q

Describe how balance is sensed?

A
  • when head rotates fluid within semicircular canals moves displacing the cupula
  • when hairs bend toward the kinocilium they increase discharge in the nerve
  • when they bend away they reduce AP firing
  • one initial rotation hairs are bent toward increasing firing
  • when the head stops rotating the hairs are bent back the other way decreasing discharge
  • canal for each plane is (X, Y & Z) on each side
  • therefore signals from right and left in all planes is sent to the brain
43
Q

Describe the structure of the utricle and saccule?

A
  • base of both there is a macula (which is otolithic)
  • utricle macula is horizontal
  • saccule macula is vertical
  • above the hair cells is a gelatinous layer in which otoliths are embedded
44
Q

What are otoliths?

A

calcium carbonate crystals

45
Q

How do utricles and saccules contribute to sensing balance?

A
  • measure linear acceleration so dependant on gravity or movement
  • if hairs move toward kinocilium increase nerve discharge
  • if move away from kinocilium decrease imoulse generation
46
Q

Where does the vestibular nucleus of the medulla connect to?

A

1) cerebellum
2) spinal cord (via vestibulospinal tract)
3) reticular formation
4) equilibrium cortex in sylvian fissure

47
Q

What is the function of the cerebellum connection?

A

cerebellum used in

  • balance
  • setting background against which predicted rapid movements can take place
48
Q

What is the function of the spinal cord connection?

A
  • muscles involved in maintenance of equilibrium
49
Q

What is the function of the reticular formation connection?

A

causing general arousal and increasing conduction speed and sensitivity in all motor nerve pools

50
Q

What is the function of the equilibrium cortex connection?

A

important in conscious sensations of equilibrium and vestibule ocular reflex and nystagmus

51
Q

What is nystagmus?

A

Pursuit - pursuit of movement of the eye during head rotation where the eye fixates on a single object
Saccade - then flicks back to it’s original when limit of eyes rotation has been reached

52
Q

What part of the vestibular system controls nystagmus?

A

Semicircular canals

53
Q

What is the pathology behind motion sickness?

A
  • there is conflicting vestibular system signals

- e.g. if reading in a car one signal is horizontal acceleration and one signals that you are stationary

Neurology (53 decks)

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