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Neuro > Auditory system > Flashcards

Auditory system Flashcards

1
Q

What is the function of a vestibular organ?

A

Capture low frequency motion (movement)

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2
Q

What is the function of a hearing organ?

A

Capture high frequency motion (sound)

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3
Q

What is the primitive mechanism of vestibular organs?

A

Statocyst - crystallised calcium ball moves freely across cells with hairs during movement which is transduced to an electrical signal

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4
Q

What are the evolved vestibular and hearing organs present in humans?

A

vestib: Utriculus and Sacculus,
audio: Cochlea and Canals

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5
Q

What relative frequencies do vestibular and hearing organs detect?

A

Vestibular - low frequency (movement), Hearing - high frequency (sound)

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6
Q

What is frequency?

A

Cycles per second
pitch (Hz)

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7
Q

What is amplitude?

A

Sound pressure, associated with physical strength
volume (dB)

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8
Q

Human range of hearing

A

20 - 20k Hz
0 - 120 dB

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9
Q

What are the structures in the outer ear?

A

Pinna,
External Acoustic Meatus,
Tympanic Membrane (eardrum)

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10
Q

What are the three functions of the outer ear?

A

Capture sound and focus to tympanic membrane Amplification of sound (by 10dB)
Protection of ear from external threats

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11
Q

What is the bony structure in the middle ear and what is its functions?

A

Ossicles - vibrate to create mechanical amplification of sound by 30dB

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12
Q

What are the muscular structures in the middle ear and what are their functions?

A

Tensor tympani muscle, Stapedius muscle
- protection by reducing sound that reaches the middle ear during loud noises

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13
Q

What is the main structure in the inner ear and what is its function?

A

Cochlea, transduce vibration signals into nervous impulses, capturing frequency and amplitude

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14
Q

What are the three compartments in the cochlea, and what do they contain?

A

Scala vestibuli
Scala tympani
scala media

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15
Q

What are the bony structures in the cochlea

A

Scala vestibuli (vestibular side)
scala tympani (basilar side)
- contain perilymph (high in Na+)

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16
Q

What is the middle membranous layer of the cochlea

A

Scala media - contains endolymph (K+),
contains the Organ of Corti (hearing organ, has hairs)

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17
Q

What are the three structures in the Organ of Corti?

A

Basilar membrane, Hair Cells, Tectorial Membrane

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18
Q

How is the basilar membrane arranged?

A

Tonotopically (like a xylophone) -
narrow base is for high frequencies, wider apex is for lower frequencies

19
Q

What type of hair cells does the Organ of Corti contain and how are they arranged?

A

Inner hair cells (in one line) and Outer hair cells (form three lines)

20
Q

What is the function of the IHC?

A

Inner hair cells - carry 95% of afferent information, transduction of sound into nerve impulses

21
Q

What is the function of the OHC?

A

Outer hair cells - carry 95% of efferent information, modulation of sensitivity of response

22
Q

What is the role of the tectorial membrane?

A

Above the hair cells, allowing hair deflection which in turn will depolarise the cell

23
Q

What are the hair cells also known as and what is the largest one called?

A

Stereocilia // Kinocilia

24
Q

How does transduction occur across the IHC?

A

Deflection of stereocilia towards kinocilia opens K+ ion channels,
cell depolarisation
Ca2+ channels open, stimulates excitatory glutamate neurotransmitter release.

Deflection of stereocilia away from kinocilia causes hyperpolarisation and inhibits nerve discharge

25
Q

Effect of amplitude on stereocilia

A

High amplitudes (volume) will cause greater deflection of stereocilia and k+ channel opening leading to greater neural signal

26
Q

Effect of frequency on stereocilia

A

Has no effect on movement of stereocilia

27
Q

Main points of transduction

A

Depolarisation - opens k+ channels
Hyperpolarisation - closes k+ channels

28
Q

How does auditory information travel from the cochlea to the cerebral hemisphere?

A

Stereocilia -> vestibulocochlear nerve’s spiral ganglions ipsilaterally to the cochlear nuclei (monoaural) in the brainstem.
bilateral superior olives
inferior colliculus.
medial geniculate body in the thalamus,
cerebral hemisphere

29
Q

What are the three types of anatomical hearing loss?

A

Conductive (outer or middle ear),
Sensorineural (cochlear or auditory nerve - 90% of cases),
Central Hearing Loss (rare, brainstem)

30
Q

What is conductive hearing loss

A

Affects outer or middle ear

31
Q

What is sensorineural hearing loss

A

affects the cochlear or auditory nerve

32
Q

What is central hearing loss

A

affects the brain and brainstem

33
Q

What are the two types of hearing loss with regards to timing?

A

Sudden hearing loss (minutes and days),
Progressive hearing loss (months to years)

34
Q

What are four causes of conductive hearing loss?

A

Outer ear - cerumen impaction (wax),
foreign body //

Middle ear - otitis (inflammation causes bubbles of liquid to be present in middle ear) ,
Otosclerosis (ossicles fuse together with age and do not vibrate properly) abnormal bone growth

35
Q

What are four causes of sensorineural hearing loss?

A

Inner ear - noise, presbycusis (old age), ototoxicity (chemotherapy, antibiotics - gentamicin)

nerve - vestibular schwannoma (acoustic neuroma)
tumour pushes on the 8th nerve causing unilateral hearing loss

36
Q

What are two quick bedside tests for clinical assessment of hearing loss?

A

Whispering numbers in ear and rubbing fingers in other ear - can they hear,

Tuning fork test

37
Q

What are the tuning fork tests and what do they show?

A

Weber test - fork on top of head, tests both ears hearing

Rinne test - on mastoid process behind ear, compares left and right hearing

38
Q

How does audiometry work?

A

Measure the patients hearing threshold - the lowest amplitude required to hear different frequencies

39
Q

What lowest levels of audiometry is normal?

A

Lowest - 10-20dB

40
Q

How can you observe conductive hearing loss on an audiometry graph?

A

Two different graphs for bone and air
Bone conduction is normal (showing there is no problems with auditory nerves) but air conduction is impaired (showing there is a problem with the outer and middle ear)

41
Q

How can you observe sensorineural hearing loss on an audiometry graph?

A

Both bone and air hearing is impacted

42
Q

How can you do newborn hearing screening?

A

Otoacoustic emissions are low-intensity sounds produced by outer hair cells as they expand and contract.

43
Q

What are the two main treatments for hearing loss?

A

Treatment of the underlying conditions (wax buildup or tumour) or hearing aids

44
Q

What are two rare treatments for hearing loss?

A

Cochlear implants and brainstem implants

Neuro (12 decks)

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