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Neuro Physiology > Vestibular Function > Flashcards

Vestibular Function Flashcards

1
Q

What is the vestibular system?

A

A sensory system essential in control of posture and balance. It is a series of fluid filled membranous tubes (labyrinths) which are embedded in the temporal bone

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2
Q

Where is the vestibular system found?

A

In the inner ear

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3
Q

What bone is the vestibular system found in?

A

Temporal bone

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4
Q

What are the semi-circular canals?

A

Organs of balance, involved in maintaining posture

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5
Q

What is the cochlea?

A

The organ of hearing

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6
Q

What makes up the vestibular apparatus?

A

3 Semi-circular canals
Utricle
Saccule

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7
Q

What is the utricle?

A

The swelling at the base of all of the 3 canals

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8
Q

What is the saccule?

A

The further swelling of endolymph underneath the utricle

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9
Q

How do the 3 semi circular canals lie in relation to each other?

A

At right angles to each other (3 dimensions)

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10
Q

What is found at the base of the semi circular canals?

A

Swellings called ampullae

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11
Q

What do ampullae contain?

A

Sensory hair cells

Cristae

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12
Q

What contains sensory hair cells?

A

Ampullae
Utricle
Saccule

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13
Q

What are the sensory organs?

A

Maculae

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14
Q

Function of sensory hair cells

A

Detect the movement of endolymph

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15
Q

What makes up the otolith organs?

A

Utricle and saccule together

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16
Q

Function of the otolith organs

A

Detect linear acceleration and encode information about the position of the head in space

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17
Q

What does the utricle detect?

A

Back/front tilt

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18
Q

What does the saccule detect?

A

Vertical movement

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19
Q

What do the semi circular canals detect?

A

Rotational acceleration

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20
Q

What are found in sensory cells in the ampullae?

A

Sensory receptors called cristae

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21
Q

What are cristae?

A

Flexible gelatinous structure called cupula that stretches across the entire width of the ampulla and responds to the movement of the endolymph fluid within the canals

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22
Q

What are found in the cupula?

A

Cilia of hair cells

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23
Q

Function of cilia of hair cells found in the cupula

A

Synapse directly with the sensory neurones of the vestibular nerve (CNVIII)

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24
Q

How do the cilia hair cells detect rotational acceleration?

A

If the skull is rotated to left or right from rest, the endolymph does not move at first because of its inertia. However the ampulla move instantly as they are embedded in the skull
The inertia of the endolymph produces drag which bends the cupula, and consequently the cilia embedded in it, in the opposite direction to the movement.
If rotate at a constant velocity, the endolymph catches up and rotates at the same speed, removing the shearing force, but this takes several seconds

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25
Q

When doing a rotational movement, what will a sudden stop cause?

A

Cause the endolymph to continue to move due to the momentum creating a continuing sense of movement and dizziness

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26
Q

What makes up the maculae?

A

Utricle

Saccule

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27
Q

What plane are the macula in the utricle orientated in?

A

Horizontal plane

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28
Q

What plane are the macula in the saccule orientated in?

A

Vertical plane

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29
Q

Features of maculae

A

Have a set of cilia
- one kinocilium
- a series of stereocilia
which protrude into the gelatinous mass called the otolith membrane

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30
Q

Function of the otolith membrane

A

Protects the cilia

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31
Q

What is embedded in the otolith membrane?

A

CaCO3 crystals called otoliths

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32
Q

Otoliths vs endolymph

A

Otoliths are much heavier than the endolymph and therefore are affected by a much greater extent by gravity during movement

33
Q

What happens when the head is tilted?

A

The otoliths and the otolith membrane are moved
This distorts the jelly
The cilia then move

34
Q

What happens when the head is tilted backwards?

A

Moves the otolith in the direction of the kinocilium causing depolarisation and increased discharge of APs.

35
Q

What happens when the head is tilted forwards?

A

Moves the otolith in the opposite direction of the kinocilium causing hyperpolarisation and a decreased discharge of APs

36
Q

What keeps the brain informed of its position in space and any direction of movement?

A

Distinct pattern of info sent from
- three cristae of semi circular canals
- two maculae of the otolith organs
Via the vestibular nerve

37
Q

What do vestibular nuclei receive input from?

A

Proprioceptors signalling limb and body position, also from neck and eye muscles

38
Q

What is kinaesthesia?

A

Perception of movement and body position

39
Q

What happens once the vestibular nerves end in the brainstem?

A

Vestibular nerve nuclei still receive input

40
Q

Two types of cilia of hair cells

A

Single very large kinocilium

Set of progressively smaller stereocilia

41
Q

What does distortion of the cilia in the direction of the kinocilium cause?

A

Depolarisation

Increased discharge of APs in the vestibular nerve

42
Q

What does distortion of the cilia away from the kinocilium lead to?

A

Hyperpolarisation

Decreased discharge of APs in the vestibular nerve

43
Q

Where does much integration of all this sensory information take place?

A

Cerebellum

44
Q

What is dynamic vestibular nystagmus?

A

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

45
Q

What is the direction of nystagmus related to?

A

The direction of the rapid flick back

R rotation -> R nystagmus

46
Q

How can nystagmus be used to test vestibular function?

A

Post rotatory nystagmus

Caloric stimulation

47
Q

What is post rotatory nystagmus?

A

Subjects rotated in a barany chair
If rotate left then during acceleration get a left nystagmus
At the end of rotation for about 20 seconds, during deceleration get a right nystagmus (due to endolymph catching up and now pushing the cupula in the opposite direction)

48
Q

What is caloric stimulation used to test?

A

Horizontal SCC

49
Q

What is caloric stimulation?

A

Outer ear washed with either cold or warm fluid

The temp difference from 37C gets through the thin bone and sets up convection currents which affects the endolymph

50
Q

What does warm fluid (44C) in caloric stimulation cause?

A

Causes nystagmus towards the affected side

51
Q

What does cold fluid (30C) in caloric stimulation cause?

A

Causes nystagmus away from the affected side

52
Q

Neumonic to remember caloric stimulation

A

COWS

  • cold opposite
  • warm same
53
Q

What would warm water into the right ear cause?

A

Right nystagmus

54
Q

What would cold water into the right ear cause?

A

Left nystagmus

55
Q

What can the stimulation of the vestibular system in the absence of movement cause?

A

Nausea and vomiting

56
Q

When can nystagmus also be seen?

A

Lesions to peripheral or central vestibular pathways

57
Q

What is kinetosis?

A

Motion sickness

58
Q

Presentation of kinetosis

A

Nausea and vomiting
Decrease in BP
Sweating
Pallor

59
Q

Pathology of kinetosis

A

Powerful maintained stimulation of the vestibular system

The cerebellum generates a “sickness signal” to the hypothalamus to bring about ANS changes

60
Q

What is the most likely cause of kinetosis?

A

If the visual and vestibular system inputs into the cerebellum are in conflict e.g. if the vestibular system indicates rotation but the visual system does not

61
Q

Presentation of labyrinthitis

A

ANS symptoms
Vertigo
Possibly nystagmus
Gross impairment of posture and balance

62
Q

What is vertigo?

A

The perception (hallucination) of movement in the absence of movement

63
Q

Presentation of Meniere’s Disease

A

Vertigo
Nausea
Nystagmus
Tinnitus

64
Q

What is Meniere’s disease associated with?

A

Overproduction of endolymph causing increased pressure

65
Q

Example of a drug that can attack the inner ear

A

Streptomycin

66
Q

What is the inner ear very sensitive to?

A

Attack by drugs

67
Q

What can happen if vestibular impairment is chronic?

A

It can be quite well compensated by the visual system

Learning circuits are set up in the cerebellum

68
Q

What can lead to nystagmus at rest?

A

Lesions in the brain stem

69
Q

What do vestibular system reflexes involve?

A

Vestibulocortical tracts

Vestibulospinal tracts

70
Q

What are the vestibular system reflexes?

A

Tonic labyrinthine reflexes
Dynamic Righting Reflexes
Vestibulo-ocular reflexes

71
Q

Function of the tonic labyrinth reflex

A

Keeps the axis of the head in a constant relationship with the rest of the body

72
Q

Where does the tonic labyrinth reflex use information from?

A

Maculae

Neck proprioceptors

73
Q

Function of the dynamic righting reflex

A

Rapid postural adjustments that made you stop falling when you trip
Long reflexes, involving extensions of all limbs

74
Q

Who is the dynamic righting reflex most evident in?

A

Cats

75
Q

How does the vestibulo-ocular reflex show the strong association between the vestibular apparatus and postural control?

A

Afferents from the semi circular canals project and connect (within the vestibular nuclei) to afferent fibres traveling to extraocular nuclei and thus have strong input into influencing eye movement
The visual system also sends powerful descending projections which controls posture

76
Q

Types of vestibulo-ocular reflexes

A

Static reflex

Dynamic vestibular reflex

77
Q

What is the static reflex?

A

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

78
Q

What is the dynamic vestibular nystagmus?

A

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

Neuro Physiology (15 decks)

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