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Year 2 - Nervous > Vestibular function > Flashcards

Vestibular function Flashcards

1
Q

What is the vestibular system + what does it consist of (3)

A

Found in the inner ear and is a series of fluid filled membranous tubes (labyrinths) which are embedded in the petrous part of the temporal bone

3 semi-circular canals, utricle and saccule

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2
Q

What is a utricle

A

swelling at the base of all 3 semicircular canals

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3
Q

What does the base of the collective 3 semicircular canals connect to

A

Utricle which then connects to the saccule

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4
Q

Semicircular canals are at what angle to each other

A

Right angle

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5
Q

What is the swelling at the base of each semi-circular canal called (NOT UTRICLE WHICH IS THE SWELLING AT THE BASE OF ALL 3 CANALS)

A

Ampulla

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6
Q

Inside the ampulla (swelling at the base of each individual semicircular canal) are sensory receptors called …

A

Cristae

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7
Q

Cristae (sensory receptors inside the ampulla) consist of a flexible gelatinous structure called the … which stretches across the entire width of the ampulla

A

Cupula

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8
Q

What does the cupula (flexible gelatinous structure inside the ampulla) respond to

A

Movement of endolymph in the semicircular canals

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9
Q

Embedded in the gelatinous cupula are … … … … … which synapse directly with the sensory neurons of the … …

A

cilia of sensory hair cells

vestibular nerve (vestibular branch of CN VIII)

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10
Q

Movement of endolymph in the semicircular canals pushes on the … therefore moving the … … … embedded within it

A

cupula

sensory hair cells

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11
Q

If head rotated left or right, endolymph in semicircular canals doesn’t move initially due to what

However, the … moves instantly

A

its inertia (tendency to remain unchanged)

ampulla

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12
Q

Inertia (tendency to remain unchanged) of endolymph causes what

A

Produces drag which bends the cupula and consequently the cilia embedded in it, in the opposite direction the head is moving

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13
Q

If you rotate at constant velocity, what does the endolymph do

However sudden stop in movement causes what effect with endolymph

A

Endolymph catches up following the initial inertia then rotates at the same speed as head movement

Endolymph still continues to move due to momentum creating a sense of movement and dizziness as eyes has told brain you’ve stopped moving but semicircular canals still tell brain you’re moving

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14
Q

2 types of cilia of sensory hair cells in the ampulla

A

Single large KINOCILIUM

Set of progressively smaller STEREOCILIA

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15
Q

Distortion of the cilia in the direction of the KINOCILIUM causes what to happen with regards to the vestibular nerve

A

DEPOLARISATION and increased discharge of APs in the vestibular nerve

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16
Q

Distortion of the cilia away from the KINOCILIUM causes what to happen with regards to the vestibular nerve

A

HYPERPOLARISATION and decreased discharge of APs in the vestibular nerve

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17
Q

Describe how hair cells in the cupola organs of the semicircular canals detect rotational acceleration (3)

A

Shearing forces act on cupula because of inertia of endolymph

Rotating at constant velocity so endolymph now rotating at same velocity as base, so no shearing forces

When rotation stops, momentum of endolymph causes shearing of cupula again but in the opposite direction to that at the start

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18
Q

What are the otolith organs (2)

A

Utricle

Saccule

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19
Q

What 2 other things contain sensory hair cells as well as the ampulla (swelling at base of each semicircular canal)

A

Utricle and saccule

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20
Q

The sensory component of semicircular canals is the ampulla, what is the equivalent for the utricle and saccule

A

Macula

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21
Q

Sensory hair cells in the macula eof the utricle/saccule detect … acceleration where the ampulla detects … acceleration

A

Linear, i.e. up/down/forward/back

Rotational

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22
Q

Sensory hair cells of the utricle detect what kind of acceleration

A

horizontal, i.e. head tilting forwards/backwards/walking

23
Q

Sensory hair cells of the saccule detect what kind of acceleration

A

vertical, i.e. up/down a lift

24
Q

The maculae of the utricle and saccule also have a set of cilia (one large kinocilium and a series of stereocilia like in the ampulla) which protrude into a gelatinous mass called the…

+ what is the equivalent of this in the ampulla

A

otolith membrane

cupula

25
Q

Embedded in the otolith membrane (cilia in the maculae of the utricle and saccule protrude into this) are what

A

Otoliths (calcium carbonate crystals)

26
Q

Otoliths (calcium carbonate crystals) embedded in the otolith membrane respond to what

A

gravitational pull

27
Q

How do the hair cells in the otolith organs (utricle and saccule) detect linear acceleration

A

Movement causes the otoliths to move which distorts the otolith membrane and therefore moves the cilia that protrude into the membrane

28
Q

Backward tilt of the head moves otoliths in the direction of what cilia

A

the kinocilium –> depolarisation and increased discharge of APs

Opposite for forward tilt

29
Q

List the 3 major sensory inputs which contribute to the perception of our body space

A
  1. Projections from the vestibular nuclei on one side project ipsilaterally, bilaterally and contra-laterally to descending motor pathways
  2. Vestibular nuclei receive input from proprioceptors signalling limb and body position,
  3. Vestibular nuclei project via the thalamus to the cerebral cortex
30
Q

What 2 tracts do the vestibular system reflexes involve

A

Vestibulocortical

Vestibulospinal

31
Q

Name 3 vestibular system reflexes

A

1) TONIC LABYRINTHE REFLEXES
2) DYNAMIC RIGHTING REFLEXES
3) VESTIBULO-OCULAR REFLEXES

32
Q

Describe what the tonic labyrinth reflex is (1) + how it works (1)

A

Keep the axis of the head in a constant relationship with the rest of the body.

Uses information from maculae and neck proprioceptors

33
Q

Describe what the dynamic righting reflex is + what animal is it most profound in

A

Rapid postural adjustments that are made to stop you falling when you trip

Cats

34
Q

Describe what the vestibulo-ocular reflex is

A

where activation of the vestibular system causes eye movement

A rotation of the head is detected, which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the muscles on the other side, thus preserving the image on the centre of the visual field

35
Q

How is the vestibular system associated with eye movement in the vestibulo-ocular reflex (2)

A

Afferents (sensory fibres) from the semi-circular canals project and connect (within the vestibular nuclei) to afferent fibres travelling to the extraocular nuclei

visual system also sends powerful descending projections which control posture and vestibular apparatus, hence increased difficulty with balancing when you close your eyes

36
Q

Name 2 vestibulo-ocular reflexes

A

Static reflex

Dynamic vestibular nystagmus

37
Q

Describe the static reflex (a type of vestibulo-ocular reflex)

A

When you tilt head, eyes intort/extort to compensate so that over a certain range, the image stays the right way up

38
Q

Describe dynamic vestibular nystagmus (a type of vestibulo-ocular reflex)

  • what is it
  • what restricts the reflex to keep occurring
A

A series of saccadic (rapid simultaneous) eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite head rotating

The extent of eye movement is restricted; when eyeball comes to the end of its range of movement, it rapidly flicks back to the zero position i.e. straight ahead

39
Q

In dynamic vestibular nystagmus (a type of vestibulo-ocular reflex), what is the direction of nystagmus

A

The direction of the rapid flick back, so right rotation of head –> right nystagmus (eyes rotate left as head rotates right then eye quickly flicks back right)

40
Q

What tests can be used to test vestibular function (2)

A

Post-rotatory nystagmus

Caloric stimulation

41
Q

Describe how a post-rotatory nystagmus test can be used to test vestibular function (2)

A

Subjects rotated in a chair, e.g. if rotated to the left then during acceleration should get a left nystagmus

At the end of rotational, for about 20 secs, during deceleration should get a right nystagmus due to endolymph catching up and rotating at same velocity so now pushing cupola in opposite direction

42
Q

Describe how a caloric stimulation test can be used to test vestibular function (2)

A

Fluid is inserted into ear
- Warm fluid (44°C) causes nystagmus TOWARDS affected side, so warm fluid in R ear –> R nystagmus

  • Cold fluid (30°C) causes nystagmus AWAY from affected side, so cold fluid in R ear –> L nystagmus
43
Q

The caloric stimulation test is used to test which semi-circular canal

A

horizontal

44
Q

Describe the COWS abbreviation for the caloric stimulation test (testing vestibular function)

A

Cold Opposite, Warm Same

  • cold fluid causes nystagmus away from affected side
  • warm fluid causes nystagmus towards affected side
45
Q

Powerful maintained stimulation of the vestibular system can give rise to

A

kinetosis = motion sickness

46
Q

Name 2 diseases that affect vestibular function

A

Labyrinthitis

Meniere’s disease

47
Q

What is labyrinthitis

A

Acute interference with normal vestibular function as a result of infection, usually viral infection

48
Q

Define vertigo

A

perception (hallucination) of movement in the absence of movement

49
Q

Presentation of labyrinthitis (5)

A 
Nausea/vomiting
Vertigo - disabling
Dizziness
Hearing loss
Nystagmus
50
Q

What is meniere’s disease + presentation (4)

A 
Episodic auditory and vestibular disease characterised by
-sudden onset of vertigo, 
- hearing loss, 
-tinnitus, and
-sensation of fullness 
in the affected ear
51
Q

Meniere’s disease cause

A

Idiopathic but thought to be associated with over-production or impaired absorption of endolymph

52
Q

List 3 damaging factors of vestibular function

A

Drugs - streptomycin
Chronic vestibular impairment
Brainstem lesion

53
Q

What drug is the inner ear sensitive to

A

Streptomycin

54
Q

If there’s chronic vestibular impairment, it can be compensated by what

A

visual system

Year 2 - Nervous (39 decks)

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