Vestiubular system

Question 1

what does teh vestibular system involve

Answer 1

series on inputs - visual, rotation and gravity (inner ear), and pressure (proprioception)

into the CNS

outputs - ocular reflex and postural control - need to be reflexes because any slower and you would fall over all the time

Question 2

describe the anatomy of the labyrinth *

Answer 2

shape carevd in bone - petrous part of the temporal bone - hardest bone of the body so dont lose balance/hearing when you hit you head

2 organs - utricle and saccule: saccule connected to the cochlear, utricle connected to the saccule

have anterior, lateral and posterior semicircular canals - the canals are all connected to the utricles

each canal has an ampulla (bigger part) and smaller part at other extremity - for anterior and posterior canals they have one end that attachesm to utricle together - this is non ampulla end

there is fluid in inner ear that moves the inner hair cells = transduction. endolymph is in teh fluid in the labyrinth, perilymph is between the organ and the bone

Question 3

describe the position of the labyrinth in the brain

Answer 3

lateral canal is horizontal

anterior canal is at 45 degrees

posterior canal is at 45 degrees posteriorly

Question 4

describe the hair cells in the labyrinth *

Answer 4

type 1 and type 2 - not separated

type 1 - more in number, direct afferent, indirect efferent, round

type 2 - direct afferents and efferents - less afferents, not round

Question 5

describe the otolith organs

Answer 5

they are the organs that do the transduction

hair cells

gelatinous matrix - on top of hair - help move the hairs because otherwise the fluid isnt dense enough

otoliths - carbonate crystals - on top of the gel - cause compression of the gel = move hair cells

Question 6

describe the striola and its significance in the otilith organs *

Answer 6

centre of the macuale, where the hair fibres change bundle polarites

hair cells have big and small kinocilia - at the striola the orientation changes - this means that when the fluid moves the cilia one side of teh maculae will be excited (ion channels open) and one side will be inhibited - therefore you can survive if you lose one part of the organ because the other side is giving the same response

the polarity is opposite in the utricle and the saccule

Question 7

describe the hair in the semicircular canals *

Answer 7

the hair cells are in the ampulla in a section called the crista

the gelatinous region is cupula - this is less dense than in te organs

kinocilia - ie the polarity of the cilia are the same throught the ampulla - however they are opposite on the other side of the ehad to allow redundance = fast responses, because inhibition of one side is interpreted.

Question 8

explain the location of the hair cells in the otolith organs *

Answer 8

in sacule they are on lateral wall to detect vertivcal movemet eg in a lift

in utricle they are on the floor and respond to movement in the horizontal plane

Question 9

describe the blood supply to the labyrinth *

Answer 9

the labyrinthine artery branches off the anterior inferior cerebellar artery, the other branch of the naterior inferior cerebllar artery goes to the brainstem and cerebellum

Question 10

describe the clinical significance of the arterial supply of the labyrinth *

Answer 10

if the pt has ear problems might be becasue of a stroke in the anterior inferior cerebellar artery - meaning there would be more problems

Question 11

describe the vestibular nerve and nuclei *

Answer 11

have superior and inferior vestibular nerves - 80% of tests for nerve function are for the superior nerve. This is a problem because if damage to inferior nerve - have no abnormal test results

primary afferents end in the vestibular nuclei - recieve info from eye, proprioception and cerebellum

the vestibular nuclei are superior, lateral, medial and inferior

superior and medial for kinetic labyrinth ie semicircular tubes

lateral and inferior for the static labyrinth ie otolith organs

the pathways reflex in the brainstem - nuclei connected to motor nuclei

Question 12

describe the vestibular pathways

Answer 12

projections to spinal nerves to limb and trunk, and upper back and neck via lateral and medial vestibulospinal tract respectively

and to nuclei of extraocular muscles to move the eye via the medial longitudinal fasiculus - oculomotor (SR MR IR), abducens nucleus (LR), trochelar nuclei (SO)

and connections forward and backward with the cerebellum via inferior cerebellar peduncle to the Flocculonodular lobe of the cerebellum

also connections with the autonomic centres - cardio and resp control - lead to nausea and cold sweats when dizzy

also go to the ventroposterior nucleus then to the vestibular cortex (location not clear) through medial leminiscus and internal capsule respectively

Question 13

what is the vestibulo-cerebellar pathway involved in

Answer 13

movement and coordination - loss of the pathway would mean you could still walk and see it would just be uncoordinated

vision ataxia

posture regulation

vestibulo-ocular reflex

Question 14

describe thalamus and cortex connections to the vestibular system

Answer 14

vestibular nuclei project to the thalamus

the thalamic nuceli project to the head region of the primary somatosensory cortex and to the superior parietal cortex - vestibular cortex involved in spatial orientation

cortical projections may account for feelings of dizzyness (vertigo) during certain kinds of vestibular stimulation

the parietal vestibular insular cortex is what is most active in vestibular responses

Question 15

describe the sections of the cerebellum involved in the vestibular system

Answer 15

the vermis and the Flocculonodular lobe are the vestibulocerebellum involved in maintenance of balanance and control of eye movement

spinocerebellum is involved in coordinating the movements

Question 16

summarise the physiology of the vestibular system

Answer 16

visual, vestibular and proprioceptive inputs

into the vestibular nuclear complex

cerebellum coorodinates this

out put through motor neurons to adjust eye movements and positional movements

Question 17

what are the functions of the vestibular system

Answer 17

postural control - done by the spinal part

to keep images fixed in retina during head movement - ie so can read on tube, and still see constant image when walking

to detect adn inform about head movements

Question 18

describe the discharge of hair cells *

Answer 18

constantly dischanging - even when there is no movement, because of gravity which is an accelaration force - this is resting discharge

when excited the frequency of discharge increases

when inhibited the frequency of discharge decreases

deflection of the kinocilia open k ion channels = increase in K = depolarisation of cell = Ca = transmission down nerve

Question 19

how does the brainstem interpret discharge

Answer 19

because of teh redundancy of the otolith organs - one side will have increased discharge when you move your head to L, other will have reduced discharge - so brainstem deduces which way the head is turned

this is for linear accelaration and tilt

Question 20

what action do the semicircular canals respond to

Answer 20

angular accelaration not velocity

endolinph inertia (ie endolinph moves in opposite dirn to the head) pushes the capulla and displaces the hair cells

they work in pairs - both horizontal are a pair, L anterior and R posterior are in the same plane, and L posterior and R anterior are in same plane

horizontal canal is at 30 degrees - need to be aware of this when testing the system

Question 21

describe the vestibulo spinal reflex pathways

Answer 21

keeps you standing

lateral vestibulospinal tract - ipsilateral, motor neurons to limb muscles

medial vestibulospinal tract - bilateral, motor neurons to the neck and back trunk

Question 22

describe the path of the lateral vestibulospinal tract

Answer 22

imput from the vision, ear and proprioception - lose one of these and lose balance eg peripheral neuropathy affect proprioceptive input

cells from the later vestibular nucleus

pathway is uncrossed and courses the entire length of the spinal chord - located in the ventral funiculus

affect ipsilateral limb muscle

cause muscles to contract to keep balance

Question 23

describe the path of the medial vestibulospinal tract

Answer 23

cells of origin are in medial vestibular nucleus

pathway is bilateral - ipsilateral is more dense

innervates cervical and upper thoracic spinal cord, influencing neck and axial muscles

Question 24

describ ethe vestibular ocular reflex

Answer 24

function - to keep images fixed

the connection is between the vestibular nuclei and oculomotor nuclei

the is a 5-7second latency

eye movement is in the opposite direction to head movement but at the same velocity and displacement

this is the fastes reflex in the body

Question 25

describe the vestibulo ocular pathways

Answer 25

for horizontal movement - information come in from scarpa’s ganglion in the inner ear - to the brainstem - send signal down CN 3 for medial and CN 6 for lateral rectus muscle - excite one set of muscles and contract the other pair so the eyes move

for vertical movement - from anterior and posterior canal to superior oblique and rectus muscle - SO CN 4, SR, IF and IO - CN 3

Question 26

describe the effect of a unilateral lesion

Answer 26

when moving - get the signal from 1 ear because of teh redundance of the system

when not moving - there is resting discharge from 1 ear and not from the other - meaning brainstem interprets that the head is moving in opposite dirn from lesion

cause eyes to move in opposite dirn to head

eyes recognise this is wrong - move back, brainstem tells them to move again

therefore repeated slow movement of eyes by central compensation, then fast movement back under visual control

Question 27

how would you diagnose vestibular problems

Answer 27

anamenesis - pts account of their history

check CN

balance and gait assessment

cerebellum - finger nose test - see if they can coordinate movement - usually have other brainstem symotoms

gaze assessment - eye movement - specific to what is damaged

vestibular tests eg caloric test, vHIT, VEMP and rotational tests - these are described well for different pathologies

CT/MRI

subjetcive assessment/questionnaires - predict long term outcome - see if the problem will cause functional problems

Question 28

what are symptoms of vestibular damage

Answer 28

vertigo - illusion of movement - usually rotational or ‘true vertigo’

dizzyness/giddyness - more vague

unsteadyness - off balance - bilateral vestibular failure

self-motion perception - eg after boat trip

Question 29

describe how vestibular disorders are categorised on location

Answer 29

peripheral - affecting labyrinth and CN 8 eg vestibular neuritis, BPPV, meniere’s disease BVF, UVF

central - affecting the CNS (brainstem/cerebellum) - eg stroke, MS, tumour

Question 30

descrive how vestibular disorders can be classified by evolution

Answer 30

acute - vestibular neuritis (labyrinthiris), stroke

intermittent - benign proximal position vertigo (BPPV)

recurrent - meniere’s disease - rare, migraine (vertigo crisis)

progressive - acoustic neuroma CN 8, degeneration with age

Question 31

what are non-vestibular causes of dizzyness

Answer 31

heart disorders

presyncopal episode

orthostatic hypotension

anaemia

hypoglycaemia

physiological

gait disorders

Question 32

what is vertigo *

Answer 32

false perception of movement in space - in the absence of physical movement

vestibular projections to the tempero-parietal spatial cortex promote perception of movement in space when there is a unilateral lesion - to the intact side

feel symptoms of intense spinning or as if on a boat

Question 33

what is oscillopsia *

Answer 33

the inability to stabalise eyes during head movement

this occurs in bilateral vestibular lesions

during a head swing - the eyes will move with the head, and then there will be multiple rapid saccades to return eyes to the right position

[if there is loss of function on one side teh VOR will be fine for movement towards the lesion, because the damaged side would be inhibited anyway, however in movement to lesioned side eyes will be taken off the target and saccades will be needed]

Question 34

what is dizzyness *

Answer 34

a sensation of unsteadiness and a feeling of movement within the head

Question 35

what is the difference between oscillopsia and vertigo *

Answer 35

vertigo occurs when you are not moving - unilateral lesion

osscillopsia occurs during movement

Question 36

descrieb vestibular nystagmus *

Answer 36

unilateral lesion

eyes move in direction away from lesion when not moving - brainstem detects this and rapidly resets the eyes

this is minimised by visual suppression mechanisms

it can be torsional and occaisionally vertical

Question 37

describe vestibular ataxia *

Answer 37

bilateral vestibular disorder - mild ataxia that is worse at speed or on uneven ground

unilateral - tendancy to lean to the to the lesioned side because of the ipsilateral vestibulo-spinal projections

Question 38

what are other consequences of vestibular lesions *

Answer 38

in acute phase of unilateral lesions = nausea and vomitinglike motion sickness - because of projections to the brain stem and the thalamus

hypotension and resp dysrhythmia - projections to the heart, peripheral vasculature and resp muscles

Impaired Sensory Integration Loss of co-ordination on directional reorientation; motion intolerance, oversensitivity to visual motion in the environment

Impairments of local navigation