Vestib - intro

Question 1

what are the 3 main functions of the vestib system

Answer 1

1. stabilize visual images on fovea of retina during head mvmts to allow clear vision
   -> gaze stability (VOR)
2. provides info used for spatial orientation
   -> sensing and perceiving motion (SCC’s hair cells, otoliths)
3. maintains postural stability during head mvmts
   -> postural control (VSR)

Question 2

what is an important challenge in assessing postural control

Answer 2

impossible to assess w/o assessing vestib

Question 3

what are 3 central processing components for postural control and which are vestibular components

Answer 3

sensory organization *
sensory adaptation *
anticipatory post control

Question 4

what are 2 motor outputs for postural control and which are vestibular components

Answer 4

VSR **
motor strategies
- ankle, hip
- stepping (ROM, ms performance, coordination)

Question 5

what are the 2 main components of the peripheral vestib system

Answer 5

vestibular labyrinth
vestibular nerve

Question 6

what are the 2 main components of the central vestib system

Answer 6

vestibular nuclei
vestibulo-cerebellum

Question 7

what are the 2 main components of perception via the vestib and what is the function of this

Answer 7

thalamus
vestib cortex

ability to perceive where we are in space, complex process requires lot of communication

Question 8

what are the main peripheral vestibular apparatus components

Answer 8

3 SCC - ant, post, lat
2 otolith organs (in vestibule)
- utricle, saccule

Question 9

function of 3 SCC vs 2 otolith organs

Answer 9

SCC = angular velocity of head
otolith = linear motion & acceleration

Question 10

where do all SCCs open at both ends to

Answer 10

the utricle

Question 11

what are the ampullas

Answer 11

expanded portion of each canal that houses vestibular receptor which can detect mvmts

Question 12

what are the cupulas: location, composition

Answer 12

w/i ampulla, at end of canal

gelatinous membrane surrounded by endolymph

Question 13

what are 3 functional components of the hair cells found in cupulas

Answer 13

1. stereocilia and kinocilia (taller)
2. cell bodies
3. afferent and efferent nere endings

Question 14

what role do the crista ampullaris hair cells embedded in the cupula play

Answer 14

hair cells will either dec or inc firing vestib nerve in order for brain to know what direction your head is rotating

Question 15

describe the process of head rotation direction being detected and relayed w/i the SCC

Answer 15

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

Question 16

what are 2 major components of hair cells

Answer 16

stereocilia
kinocilium

Question 17

direction of cupular deflection and what response is created

Answer 17

deflection of stereocilia TOWARDS kinocilium EXCITES CN VIII

deflection of stereocilia AWAY from kinocilium INHIBITS CN VIII

Question 18

what is the constant firing rate of hair signals in the cupula at rest and what is the significance

Answer 18

70-100 spikes/sec

allows system to be capable of detecting mvmt

Question 19

what is the significance of the speed of head rotation

Answer 19

the quicker you move, the more displacement of cupula and brain is able to detect speed and more accurately the deflection

Question 20

what are the 2 functions of the otolith organs

Answer 20

static head tilt (gravity)
linear acceleration/decel (inertia)

Question 21

what is the composition of the otolith organs

Answer 21

otolithic membrane made up of otoconia and gelatinous layer

hair cells bend when otoconia displaced relative to head

Question 22

where does info from the peripheral vestib system go to and what happens next

Answer 22

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.

Question 23

what are the divisions of the vestibular nerve and what do they each innervate

Answer 23

superior vestib nerve
- lateral SCC
- anterior SCC
- utricle

inferior vestib nerve
- posterior SCC
- saccule

Question 24

what are the 5 main vestib system projections

Answer 24

thalamus
parietoinsular vestib cortex (PIVC)
cerebellum
VSR
VOR

Question 25

what are the 2 central vestibular projections

Answer 25

thalamus
parietoinsular vestib cortex (PIVC)

Question 26

what are the functions of the thalamus vestib projection

Answer 26

allows for discrimination b/w self mvmt vs that of environment

multisensory integration for postural control

Question 27

what is the parietoinsular vestib cortex (PIVC)

Answer 27

junction of parietal and insular lobe

Question 28

what are the functions of the PIVC vestib projection

Answer 28

multisensory integration of vestib info w somatosensory and visual input

help body sense where it is in space (spatial identification)

Question 29

how and where are vestib motor projections carried

Answer 29

via CN VIII to vestib nuclear complex

Question 30

what are the 2 main motor projections and where are each roughly sent to

Answer 30

VOR and VSR
- VOR = higher neural centers
- VSR = lower neural centers

Question 31

what is the purpose of the VSR

Answer 31

coordinate head and neck mvmt w trunk and body
- goal = maintain head in upright position

Question 32

what are the 2 distinct VSR pathways and their specific functions

Answer 32

lateral vestibulospinal
- postural changes to compensate for tilts and mvmts of body

medial vestibulospinal
- orients & stabilizes head w respect to gravity

Question 33

what is the pathway to trigger the VSR and then once the VSR to be enacted

Answer 33

1. head tilts -> stim SCCs and otoliths vestib receptors -> deflects hair cells w/i otoliths
2. vestib n. and vestib nuclei activated -> transmit impulses via lateral and medial vestib spinal tracts
3. extensor activity induced to side of head tilt & flexor activity to opposite side

Question 34

what is the purpose of the VOR

Answer 34

maintain stable gaze reflex during head mvmt

Question 35

what are the components of the VOR

Answer 35

3 neuron arc via MLF
- vestib/scarpas ganglion
- vestib nuclei
- oculomotor nuclei

Question 36

what is the pathway to trigger the VOR from a R head turn and then once the VOR to be enacted

Answer 36

1. head turn to R, endolymphatic flow deflects cupula to L
2. dc rate from hair cells in R crista inc, dc rate from hair cells in L crista dec
3. changes in firing rate transmitted to vestib n. and influence dc from vestib nuclei to cerebellum
4. excitatory impulses transmitted via white matter tracts to oculomotor ms, compensatory eye mvmts to L
5. if eye and head velocity not 1:1, CNS will detect and reduce error
6. VOR acts to maintain gaze stability

Question 37

what ms pair does the anterior canal innervate

Answer 37

ipsi = superior rectus
contra = inferior oblique

Question 38

what ms pair does the posterior canal innervate

Answer 38

ipsi = superior oblique
contra = inferior rectus

Question 39

what ms pair does the lateral canal innervate

Answer 39

ipsi = medial rectus
contra = lateral rectus