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Neuro > Audio-vestibular system > Flashcards

Audio-vestibular system Flashcards

1
Q

What did a Statocyst evolve into?

A

Utriculus –> Sacculus –> Cochlea and Canals

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2
Q

What is a vestibular organ?

A

Captures low frequency motion (movements)

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3
Q

What is a hearing organ?

A

Captures high frequency motion (sounds)

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4
Q

What is frequency / pitch?

A

(Hz): Cycles per second, perceived tone.

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5
Q

What is amplitude / loudness?

A

(dB): Sound pressure, subjective attribute correlated with physical strength.

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6
Q

What is the range of human hearing?

A

Frequency: 20–20,000Hz
Loudness: 0 dB to 120 dB sound pressure level (SPL)

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7
Q

What are the outer ear functions?

A

To capture sound and to focus it to the tympanic membrane.
Modest amplification (10DB) of upper range of speech frequencies by resonance in the canal.
To protect the ear from external threats.

Pinna–> External auditory meatus –> Tympanic membrane

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8
Q

What is the function of the middle ear?

A

Tympani membrane –> Oval window

Mechanical amplification (can provide an additional 20-30dB)

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9
Q

What happens at the tympanic membrane?

A

Vibrations in the air are changed to mechanical movement and now moves at the exact frequency of sound

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10
Q

What happens when the sound is too loud in the middle ear?

A

Tensor tympani muscle and stapedius muscle both contract

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11
Q

What is the function of the inner ear?

A

The hearing part of the inner ear is the cochlea
Its function is to transduce vibration into nervous impulses
It does so in a way that captures the frequency (or pitch) and intensity (or loudness) of the sound

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12
Q

What is the cochlea composed for?

A

The cochlea contains 3 compartments:

-Scala vestibuli and scala tympani: Bone structures, contain perilymph (high in sodium)
-Scala media: Membranous structure, contains endolymph (high in potassium). Here is where the hearing organ or Organ of Corti is located.

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13
Q

What is the basilar membrane?

A

The structure where the organ of Corti lies in is the basilar membrane
Basilar membrane is arranged tonotopically, using the same principle as a xylophone

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14
Q

What type of hair cells does the organ of Corti contain?

A

Inner hair cells (1 line)
Outer hair cells (3 lines)

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15
Q

Where is the tectorial membrane?
What does it do?

A

The tectorial membrane is above the hair cells and allows hair deflection, which in turn will depolarise the cell.

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16
Q

What do the inner hair cells do?

A

Carry 95% of the afferent information of the auditory nerve. Their function is the transduction of the sound into nerve impulses

Carry the information via the auditory nerve once you get the signal. First stage of transduction from a motion to a neuronal signal here

To spiral ganglion cells and then to the auditory nerve

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17
Q

What do the outer hair cells do?

A

Carry 95% of efferents of the auditory nerve. Their function is modulation of the sensitivity of the response.

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18
Q

How does transduction occur?

A

The hairs of the hair cells are called stereocilia.
The deflection of the stereocilia towards the longest cilium (kinocilium) will open K+ channels and the voltage gated Ca2+ channels open, with Ca 2+ entering
This depolarises the cell releasing the neurotransmitter to the afferent nerve which then depolarises.

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19
Q

How does higher amplitude affect deflection?

A

Higher amplitudes (louder) of sound will cause greater deflection of stereocilia and K+ channel opening

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20
Q

What happens in depolarisation
What happens in hyperpolarisation?

A

Opens K+ channels (upward phase)
Closes K+ channels (downward phase)

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21
Q

Explain the auditory pathways*

A

Auditory nerve combines with the vestibular-cochlear never (8th cranial nerve) to the ipsilateral cochlear nuclei in the brainstem (pons)

Sends a message when it gets to cochlear nuclei to the other side and also to superior olive

Auditory information crosses at the superior olive level

After this point all connection are bilateral

Superior olive connects to inferior colliculus in brain stem

This then connects with medial geniculate in thalamus

Then to auditory cortex in temporal lobe

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22
Q

Why does brain damage affect a small part and why is it rare to lose hearing

A

Because it is bilaterally innervated very early stage in pons

23
Q

Why does brain damage only affect a small part

A

Bilaterally innervated at very early stage in pons

24
Q

Where in the thalamus is related to hearing

A

Medial geniculate body

25
Q

What are anatomical types of hearing loss

A

Conductive hearing loss: Problem is located in outer or middle ear.
Sensorineural hearing loss: The sensory organ (cochlear) or the nerve (auditory nerve). (90% of all hearing loss!)
Central hearing loss: Very rare and originates in the brain and brainstem

26
Q

What are the timing types of hearing loss

A

Sudden hearing loss minutes to days
Progressive hearing loss months to years

27
Q

What are the causes of conductive hearing loss

A

Outer ear:
Wax
Foreign body

Middle ear:
Otitis - inflammation due to infection - Bubbles can be seen through the ear drum, suggesting there is liquid inside the middle ear.
Otosclerosis - joints fusing

28
Q

What are the causes of sensorineural hearing loss

A

Inner ear:
Noise
Presbycusis (old age)
Ototoxicity - chemotherapy / antibiotics e.g. gentamycin

Nerve:
acoustic neuroma (vestibular schwannoma) (unilateral)

29
Q

What are examples of clinical test

A

Bedside tests are quick but not accurate-Whisper in ipsilateral ear whilst rubbing fingers in contralateral ear

Tuning Fork – 2 tests assess the presence of gross hearing loss.
-Weber test - top
-Rinne test - on mastoid, behind ear

30
Q

What is an audiogram

A

The audiogram is where the hearing thresholds are plotted to define if there is a hearing loss or not. A normal hearing threshold is located between 0 – 20dB

31
Q

What is conductive hearing loss

A

Can hear through headphones as going directly through bone to inner ear, organ of corti, and inner ear works so neurone problem

32
Q

What is a a special test in audiometry that can be done

A

Otoacoustic Emissions (OAEs)

The normal cochlea produces low-intensity sounds called OAEs
These sounds are produced specifically by the outer hair cells as they expand and contract
This test is often part of the newborn hearing screening and hearing loss monitoring.

33
Q

What is the treatment for hearing problems

A

Underlying cause e.g. treat infection
Hearing aids
Cochlear implants
Brainstem implants

34
Q

What goes into the vestibular system

What comes out

A

Movement and gravity
-Via mechanical sensors (canals and otoliths)

The CNS integrates this information and generates responses

The outputs are perception and reflexes that maintain posture and gaze
-Ocular reflex and postural control

35
Q

What is the vestibular organ made of

A

The utricule and saccule are located in the vestibule and are joined by a conduit. The saccule is also joined to the cochlea

There are three semicircular canals on each ear, anterior, posterior and lateral

The semicircular canals have an ampulla on one side, and they are connected to the utricle.

36
Q

What are otolith organs

A

Utricle and saccule are the otolith organs. Their cells are located on the maculae, placed horizontally in the utricle and vertically in the saccule

37
Q

What are maculae

A

The maculae contain the hair cells, a gelatinous matrix and the otoliths on top. These otholiths are carbonate crystals that help the deflection of the hairs.

38
Q

What is otolith movement

What is horizontal movement

What is vertical movement

A

Linear acceleration and tilt

Utricule

Saccule

39
Q

Describe the semi-circular canals

A

The hair cells in the canals are located in the ampulla. The rest of the canal only has a liquid high in potassium called endolymph

The ampulla has the crista, where the hair cells are located. The cells are surrounded by the cupula which helps the hair cell movement

39
Q

Describe the semi-circular canals

A

The hair cells in the canals are located in the ampulla. The rest of the canal only has a liquid high in potassium called endolymph

The ampulla has the crista, where the hair cells are located. The cells are surrounded by the cupula which helps the hair cell movement

40
Q

Describe the orientation of the canals

A

The orientation of the canals in the head defines three planes.

Anterior and posterior canals form a 90° angle. Lateral canals are horizontal to the other canals.

Therefore they work in pairs

41
Q

Describe the hair cells and how they work

A

Vestibular hair cells have a kinocilium (the biggest cilium) and stereocilia
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement

42
Q

Describe hair cell potentials

A

Hair cells have a resting potential which has a basal discharge to the nerve
Hairs moving towards the kinocilium generates depolarization and an increase in nerve discharge.
Hairs moving away from the kinocilium generates hyperpolarization and a reduction in nerve discharge.

43
Q

What are the vestibular system functions

A

To detect and inform about head movements
Balance
To keep images fixed in the retina during head movements

44
Q

What are the vestibular reflexes

A

Vestibulo-ocular Reflex
(VOR)

Vestibulo Spinal Reflex
(VSR)

45
Q

Describe the vestibulo-ocular relfex

A

Keeps images fixed in the retina
Connection between vestibular nuclei and oculomotor nuclei
Eye movement in opposite direction to head movement, but same velocity and amplitude

46
Q

How to categorise vestibular disorders

A

Timing and Laterality

In acute AND unilateral:
Main complaints - imbalance, dizziness, vértigo and nausea

In slow AND unilateral or any bilateral loss:
Main complaints – imbalance and nausea – NO vertigo

47
Q

Where are peripheral vestibular disorders and give some examples

A

Vestibular organ and/or VIII nerve

Vestibular neuritis
Benign Paroxysmal Positional Vertigo (BPPV)
Meniere’s disease

48
Q

Where are central vestibular disorders and give some examples

A

CNS (brainstem/cerebellum)

Stroke
Multiple Sclerosis
Tumours

49
Q

Explain the clinical approach for a physician

A

The main diagnoses

BPPV (crystals moving)
Vestibular Neuritis
Vestibular Migraine
Stroke (cerebellar)

The core exam

EYES
EARS
LEGS

Red Flags
Headache
Gait problems
Hyper-acute onset
Hearing loss
Prolonged symptoms (>4 days)

50
Q

What are the balance disorders in terms of timing

A

Acute:
Vestibular Neuritis
Stroke
HINTS exam

Intermittent:
Benign Paroxysmal Positional Vertigo (BPPV)
Dix-Hallpike test

Recurrent:
Migraine
(Meniere’s Disease)

Progressive:
Schwannoma vestibular (VIIIth nerve)
Degenerative conditions (MS)

51
Q

Explain the HINTS exam

A

HeadImpulseTest​
Horizontal rotational VOR
**Vestibular Neuritis or Stroke?

Nystagmus​
Vestibular organ Vs Cerebellar/brainstem nystagmus

TestofSkewDeviation​
Verticalmisalignment - usually absent in peripheral pathology

52
Q
A

Vestibular nerve goes to ganglion and joins with the auditory nerve and goes together with auditory nerve as vestibulo-cochlear nerve into brain through pons

Vestibular nerve goes through vestibuli nuclei, then cerebellum and then nuclei of eye movement - 3rd, 4th and 6th nerves that control eyes

Neuro (8 decks)

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