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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
When doing a rotational movement, what will a sudden stop cause?
Cause the endolymph to continue to move due to the momentum creating a continuing sense of movement and dizziness
26
What makes up the maculae?
Utricle | Saccule
27
What plane are the macula in the utricle orientated in?
Horizontal plane
28
What plane are the macula in the saccule orientated in?
Vertical plane
29
Features of maculae
Have a set of cilia - one kinocilium - a series of stereocilia which protrude into the gelatinous mass called the otolith membrane
30
Function of the otolith membrane
Protects the cilia
31
What is embedded in the otolith membrane?
CaCO3 crystals called otoliths
32
Otoliths vs endolymph
Otoliths are much heavier than the endolymph and therefore are affected by a much greater extent by gravity during movement
33
What happens when the head is tilted?
The otoliths and the otolith membrane are moved This distorts the jelly The cilia then move
34
What happens when the head is tilted backwards?
Moves the otolith in the direction of the kinocilium causing depolarisation and increased discharge of APs.
35
What happens when the head is tilted forwards?
Moves the otolith in the opposite direction of the kinocilium causing hyperpolarisation and a decreased discharge of APs
36
What keeps the brain informed of its position in space and any direction of movement?
Distinct pattern of info sent from - three cristae of semi circular canals - two maculae of the otolith organs Via the vestibular nerve
37
What do vestibular nuclei receive input from?
Proprioceptors signalling limb and body position, also from neck and eye muscles
38
What is kinaesthesia?
Perception of movement and body position
39
What happens once the vestibular nerves end in the brainstem?
Vestibular nerve nuclei still receive input
40
Two types of cilia of hair cells
Single very large kinocilium | Set of progressively smaller stereocilia
41
What does distortion of the cilia in the direction of the kinocilium cause?
Depolarisation | Increased discharge of APs in the vestibular nerve
42
What does distortion of the cilia away from the kinocilium lead to?
Hyperpolarisation | Decreased discharge of APs in the vestibular nerve
43
Where does much integration of all this sensory information take place?
Cerebellum
44
What is dynamic vestibular nystagmus?
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
What is the direction of nystagmus related to?
The direction of the rapid flick back | R rotation -> R nystagmus
46
How can nystagmus be used to test vestibular function?
Post rotatory nystagmus | Caloric stimulation
47
What is post rotatory nystagmus?
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
What is caloric stimulation used to test?
Horizontal SCC
49
What is caloric stimulation?
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
What does warm fluid (44C) in caloric stimulation cause?
Causes nystagmus towards the affected side
51
What does cold fluid (30C) in caloric stimulation cause?
Causes nystagmus away from the affected side
52
Neumonic to remember caloric stimulation
COWS - cold opposite - warm same
53
What would warm water into the right ear cause?
Right nystagmus
54
What would cold water into the right ear cause?
Left nystagmus
55
What can the stimulation of the vestibular system in the absence of movement cause?
Nausea and vomiting
56
When can nystagmus also be seen?
Lesions to peripheral or central vestibular pathways
57
What is kinetosis?
Motion sickness
58
Presentation of kinetosis
Nausea and vomiting Decrease in BP Sweating Pallor
59
Pathology of kinetosis
Powerful maintained stimulation of the vestibular system | The cerebellum generates a "sickness signal" to the hypothalamus to bring about ANS changes
60
What is the most likely cause of kinetosis?
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
Presentation of labyrinthitis
ANS symptoms Vertigo Possibly nystagmus Gross impairment of posture and balance
62
What is vertigo?
The perception (hallucination) of movement in the absence of movement
63
Presentation of Meniere's Disease
Vertigo Nausea Nystagmus Tinnitus
64
What is Meniere's disease associated with?
Overproduction of endolymph causing increased pressure
65
Example of a drug that can attack the inner ear
Streptomycin
66
What is the inner ear very sensitive to?
Attack by drugs
67
What can happen if vestibular impairment is chronic?
It can be quite well compensated by the visual system | Learning circuits are set up in the cerebellum
68
What can lead to nystagmus at rest?
Lesions in the brain stem
69
What do vestibular system reflexes involve?
Vestibulocortical tracts | Vestibulospinal tracts
70
What are the vestibular system reflexes?
Tonic labyrinthine reflexes Dynamic Righting Reflexes Vestibulo-ocular reflexes
71
Function of the tonic labyrinth reflex
Keeps the axis of the head in a constant relationship with the rest of the body
72
Where does the tonic labyrinth reflex use information from?
Maculae | Neck proprioceptors
73
Function of the dynamic righting reflex
Rapid postural adjustments that made you stop falling when you trip Long reflexes, involving extensions of all limbs
74
Who is the dynamic righting reflex most evident in?
Cats
75
How does the vestibulo-ocular reflex show the strong association between the vestibular apparatus and postural control?
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
Types of vestibulo-ocular reflexes
Static reflex | Dynamic vestibular reflex
77
What is the static reflex?
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
What is the dynamic vestibular nystagmus?
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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