Vestib - intro Flashcards
what are the 3 main functions of the vestib system
- stabilize visual images on fovea of retina during head mvmts to allow clear vision
-> gaze stability (VOR) - provides info used for spatial orientation
-> sensing and perceiving motion (SCC’s hair cells, otoliths) - maintains postural stability during head mvmts
-> postural control (VSR)
what is an important challenge in assessing postural control
impossible to assess w/o assessing vestib
what are 3 central processing components for postural control and which are vestibular components
sensory organization *
sensory adaptation *
anticipatory post control
what are 2 motor outputs for postural control and which are vestibular components
VSR **
motor strategies
- ankle, hip
- stepping (ROM, ms performance, coordination)
what are the 2 main components of the peripheral vestib system
vestibular labyrinth
vestibular nerve
what are the 2 main components of the central vestib system
vestibular nuclei
vestibulo-cerebellum
what are the 2 main components of perception via the vestib and what is the function of this
thalamus
vestib cortex
ability to perceive where we are in space, complex process requires lot of communication
what are the main peripheral vestibular apparatus components
3 SCC - ant, post, lat
2 otolith organs (in vestibule)
- utricle, saccule
function of 3 SCC vs 2 otolith organs
SCC = angular velocity of head
otolith = linear motion & acceleration
where do all SCCs open at both ends to
the utricle
what are the ampullas
expanded portion of each canal that houses vestibular receptor which can detect mvmts
what are the cupulas: location, composition
w/i ampulla, at end of canal
gelatinous membrane surrounded by endolymph
what are 3 functional components of the hair cells found in cupulas
- stereocilia and kinocilia (taller)
- cell bodies
- afferent and efferent nere endings
what role do the crista ampullaris hair cells embedded in the cupula play
hair cells will either dec or inc firing vestib nerve in order for brain to know what direction your head is rotating
describe the process of head rotation direction being detected and relayed w/i the SCC
forces from head mvmt pushes endolymph fluid opposite direction
-> deflects cupula & contained sensory hair cells also in opposite direction to rotation
that excites or inhibits signalling to vestib nerve in order for us to know where our heads are in space
what are 2 major components of hair cells
stereocilia
kinocilium
direction of cupular deflection and what response is created
deflection of stereocilia TOWARDS kinocilium EXCITES CN VIII
deflection of stereocilia AWAY from kinocilium INHIBITS CN VIII
what is the constant firing rate of hair signals in the cupula at rest and what is the significance
70-100 spikes/sec
allows system to be capable of detecting mvmt
what is the significance of the speed of head rotation
the quicker you move, the more displacement of cupula and brain is able to detect speed and more accurately the deflection
what are the 2 functions of the otolith organs
static head tilt (gravity)
linear acceleration/decel (inertia)
what is the composition of the otolith organs
otolithic membrane made up of otoconia and gelatinous layer
hair cells bend when otoconia displaced relative to head
where does info from the peripheral vestib system go to and what happens next
higher sensors - vestib and nuclear complexes in medulla and vestib cerebellum
- relayed for further integration w other sensory info and related info ab our physical state, environment, etc.
what are the divisions of the vestibular nerve and what do they each innervate
superior vestib nerve
- lateral SCC
- anterior SCC
- utricle
inferior vestib nerve
- posterior SCC
- saccule
what are the 5 main vestib system projections
thalamus
parietoinsular vestib cortex (PIVC)
cerebellum
VSR
VOR
what are the 2 central vestibular projections
thalamus
parietoinsular vestib cortex (PIVC)
what are the functions of the thalamus vestib projection
allows for discrimination b/w self mvmt vs that of environment
multisensory integration for postural control
what is the parietoinsular vestib cortex (PIVC)
junction of parietal and insular lobe
what are the functions of the PIVC vestib projection
multisensory integration of vestib info w somatosensory and visual input
help body sense where it is in space (spatial identification)
how and where are vestib motor projections carried
via CN VIII to vestib nuclear complex
what are the 2 main motor projections and where are each roughly sent to
VOR and VSR
- VOR = higher neural centers
- VSR = lower neural centers
what is the purpose of the VSR
coordinate head and neck mvmt w trunk and body
- goal = maintain head in upright position
what are the 2 distinct VSR pathways and their specific functions
lateral vestibulospinal
- postural changes to compensate for tilts and mvmts of body
medial vestibulospinal
- orients & stabilizes head w respect to gravity
what is the pathway to trigger the VSR and then once the VSR to be enacted
- head tilts -> stim SCCs and otoliths vestib receptors -> deflects hair cells w/i otoliths
- vestib n. and vestib nuclei activated -> transmit impulses via lateral and medial vestib spinal tracts
- extensor activity induced to side of head tilt & flexor activity to opposite side
what is the purpose of the VOR
maintain stable gaze reflex during head mvmt
what are the components of the VOR
3 neuron arc via MLF
- vestib/scarpas ganglion
- vestib nuclei
- oculomotor nuclei
what is the pathway to trigger the VOR from a R head turn and then once the VOR to be enacted
- head turn to R, endolymphatic flow deflects cupula to L
- dc rate from hair cells in R crista inc, dc rate from hair cells in L crista dec
- changes in firing rate transmitted to vestib n. and influence dc from vestib nuclei to cerebellum
- excitatory impulses transmitted via white matter tracts to oculomotor ms, compensatory eye mvmts to L
- if eye and head velocity not 1:1, CNS will detect and reduce error
- VOR acts to maintain gaze stability
what ms pair does the anterior canal innervate
ipsi = superior rectus
contra = inferior oblique
what ms pair does the posterior canal innervate
ipsi = superior oblique
contra = inferior rectus
what ms pair does the lateral canal innervate
ipsi = medial rectus
contra = lateral rectus
