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NEURO > Vestibular function > Flashcards

Vestibular function Flashcards

1
Q

what is the vestibular system

A

sensory system essential in the control of posture and balance

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2
Q

what is the vestibular system and where is it found

A

inner ear - series of fluid filled membraneous tubes (labyrinths) that are embedded in the temporal bone

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3
Q

what are the components of the vestibular apparatus

A

3 semi-circualr canals - at right angles to each other

utricle

saccule

all contain sensory hair cells

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4
Q

what are the otolith organs

A

the utricle and saccule collectively

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5
Q

what do the otolith organs detect

A

Both:
linear accelleration
encode info about the position of the head in space

utricle - back/front head tilt

saccule - vertical movement

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6
Q

what do the semicircular canals (SSC)

A

detect rotational acceleration

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7
Q

what is the structure of the SSC

A

filled with endolymph fluid - contain sensory cells in swellings (cristae) at the base (ampulla) of the bony canals

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8
Q

what is contained in the cristae

A

flexible gelatinous structure called the cupula - stretches across entrire width of the ampulla

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9
Q

what does the cupula respond to

A

movement of endolymph fluid within the canals

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10
Q

what are found in the base of the cupula

A

cilia of hair cells that synapse with the sensory neurones of the vestibular nerve

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11
Q

how do the SSC canals detect rotational acceleration

A
  1. skull rotated right or left
  2. ampulla moves as it is embedded in the skull
  3. BUT endolymph does not move at first (inertia)
  4. inertia produces drag which bends the cupula and and ciliary in it in the opposite direction
  5. constant velocity - endolymph catches up and rotates at same speed - cupula and ciliary no longer bending

sudden stop:

  1. causes endolymph to carry on moving in same direction
  2. drag of cupula in opposite direction
  3. creates continuing sense of movement and dizziness
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12
Q

what are the two types of cilia of the hair cells

A

single large kinocilium

progressively smaller stereocilia

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13
Q

how does movement of the cilia allow the brain to determine its position in time and scape

A

movement of the cilia in different directions causes depolarisation or hyperpolarisation of the vestibular nerve

all cupula orientated slightly differently so the brain can build up a 3D image of body position form pattern of firing and inhibition

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14
Q

what happens when the cilia distort TOWARDS the kinocilium

A

DEPOLARISATION

increases discharge of APs in the vestibular nerve

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15
Q

what happens when the cilia distort AWAY from the kinocilium

A

HYPERPOLARISATION

decreased discharge of APs in the vestibular nerve

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16
Q

where does integration of this sensory information from the cilia and vestibular nerve take place

A

cerebellum

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17
Q

what are the sensory apparatus of the saccule and utricle known as

A

maculae

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18
Q

how are macula orientated

A

utricle - horizontal plane

saccule - vertical plane

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19
Q

what is the structure of the maculae

A

set of cilia (single kinocilium, series of stereo cilium) protrude into otolith membrane

crystals called otoliths are embedded on other side of the membrane

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20
Q

what detects tilting of the head

A

macula in the utricle (horizontal plane)

otoliths have greater density than endolymph - more affected by gravity - otoliths moving move membrane - membrane moving moves cilia

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21
Q

how is a backwards tilt detected

A

moves otoliths TOWARDS kinocilium

depolarisation and increased APs in vestibular nerve

22
Q

how is a forward tilt detected

A

moves otoliths AWAY from kinocilium

hyperpolarisation and decreased APs in vestibular nerve

23
Q

what detects vertical forces (e.g. movement in a lift)

A

macula in saccule

also provide info on orientation of the head when lying down

24
Q

where do projections from the vestibular nuclei project

A

ipsilaterally, bilaterally and contra-laterally to descending motor pathways

also extraocular nuclei (extraocular muscles)

25
Q

where do vestibular nuclei receive input from

A

proprioceptors signalling limb and body position

also from neck and eye muscles

26
Q

how do we get kinaesthesia

A

kinaesthesia = perception of movement and body position

from vestibular nuclei projecting via the thalamus to the cerebral cortex

27
Q

what tracts do vestibular system reflexes involve

A

vestibulocortical and vestibulospinal tracts

28
Q

what are the three vestibular system reflexes

A

tonic labyrinthine relfex

dynamic righting relfex

vestibulo-occular reflexs

29
Q

what is the tonic labyrinthine reflex

A

keeps axis of head in constant relationship with the body - use info from maculae and neck proprioceptors

30
Q

what is the dynamic righting reflex

A

rapid postural adjustments made to stop you falling when you trip - long reflexes involving extension of all limbs

31
Q

how does info from the vestibular system affect eye movement

A

afferents from the semi circular canals connect in the vestibular nuclei to afferents travelling to the extraocular nuclei

= influence eye movement

32
Q

why might you have increased difficulty balancing when closing your eyes

A

visual system sends descending projections which control posture

33
Q

how is the balance of people with damaged vestibular apparatus affected

A

can still maintain balance when eyes open

immediately lost on closing eyes

34
Q

what are the two vestibulo-ocular reflexes

A

static reflex

dynamic vestibular nystagmus

35
Q

what is the static reflex

A

when you tilt your head - eyes intort/extort to compensate

36
Q

what is dynamic vestibular nystagmus

A

series of saccadic eye movements - rotate eye against the direction of rotation of the head so that original direction of gaze is preserved

37
Q

what is the conventional direction of nystagmus

A

right rotation = right nystagmus

vice versa

38
Q

how can nystagmus be used to test vestibular function

A

post -rotatory nystagmus

caloric stimulation

39
Q

what is seen during post-rotatory nystagmus

A

left rotation - during acceleration = left nystagmus

end of rotation - deceleration = right nystagmus

due to endolymph catching up and pushing chapel in opposite direction

40
Q

what is caloric stimulation nystagmus

A

test for horizontal SSC

when outer ear washed with warm or cold water - temp gets through thin bone and sets up convection current to move endolymph

warm into R ear = R nystagmus

cold into R ear = L nystagmus

41
Q

when can nystagmus be seen pathologically

A

lesions to peripheral or central vestibular pathways

42
Q

what is kinetosis and what causes it

A

motion sickeness

caused by maintained stimulation of the vestibular system

if visual and vestibular inputs to cerebellum are in conflict e.g. vestibular indicates rotation but visual does not

43
Q

what are the symptoms of kinetosis and how are they brought about

A

nausea, vomiting, deceased BP, dizziness, sweating, pallor

when conflict between visual/vestibular - cerebellum generates “sickness signal” to hypothalamus - brings about ANS changes

44
Q

what does labyrinthitis cause

A

acute interference with normal vestibular function = all ANS symptoms and vertigo

45
Q

what is vertigo

A

perception of movement in the absence of movement

46
Q

what is involved in menieres disease

A

overproduction of endolymph causing increase pressure = vertigo, nausea, nystagmus, tinnitus

47
Q

what is tinnitus

A

subjective noise

48
Q

give an example of a drug that can attack the inner ear

A

streptomycin

49
Q

how can chronic vestibular function be compensated for

A

by the visual system - learning circuits can be set up in the cerebellum

*problems if subjects cannot use visual info

50
Q

what can lad to nystagmus at rest

A

lesions of the brainstem

NEURO (51 decks)

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