Vestiubular system Flashcards
what does teh vestibular system involve
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
describe the anatomy of the labyrinth *
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
describe the position of the labyrinth in the brain
lateral canal is horizontal
anterior canal is at 45 degrees
posterior canal is at 45 degrees posteriorly
describe the hair cells in the labyrinth *
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
describe the otolith organs
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
describe the striola and its significance in the otilith organs *
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
describe the hair in the semicircular canals *
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.
explain the location of the hair cells in the otolith organs *
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
describe the blood supply to the labyrinth *
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
describe the clinical significance of the arterial supply of the labyrinth *
if the pt has ear problems might be becasue of a stroke in the anterior inferior cerebellar artery - meaning there would be more problems
describe the vestibular nerve and nuclei *
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
describe the vestibular pathways
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
what is the vestibulo-cerebellar pathway involved in
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
describe thalamus and cortex connections to the vestibular system
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
describe the sections of the cerebellum involved in the vestibular system
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
summarise the physiology of the vestibular system
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
what are the functions of the vestibular system
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
describe the discharge of hair cells *
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
how does the brainstem interpret discharge
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
what action do the semicircular canals respond to
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
describe the vestibulo spinal reflex pathways
keeps you standing
lateral vestibulospinal tract - ipsilateral, motor neurons to limb muscles
medial vestibulospinal tract - bilateral, motor neurons to the neck and back trunk
describe the path of the lateral vestibulospinal tract
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
describe the path of the medial vestibulospinal tract
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
describ ethe vestibular ocular reflex
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
describe the vestibulo ocular pathways
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
describe the effect of a unilateral lesion
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
how would you diagnose vestibular problems
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
what are symptoms of vestibular damage
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
describe how vestibular disorders are categorised on location
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
descrive how vestibular disorders can be classified by evolution
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
what are non-vestibular causes of dizzyness
heart disorders
presyncopal episode
orthostatic hypotension
anaemia
hypoglycaemia
physiological
gait disorders
what is vertigo *
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
what is oscillopsia *
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]
what is dizzyness *
a sensation of unsteadiness and a feeling of movement within the head
what is the difference between oscillopsia and vertigo *
vertigo occurs when you are not moving - unilateral lesion
osscillopsia occurs during movement
descrieb vestibular nystagmus *
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
describe vestibular ataxia *
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
what are other consequences of vestibular lesions *
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
