part 5 Flashcards
what does the vestibulopsinal tract do
controls postural orientation
- collaborates with reflexes elicited by stimulation of the vestibular and visual reflexes
what are the components of the vestibulospinal tract
vestibulospinal reflex
vestibulocolic reflex
what does the VSR do
gathers static and dynamic reflexes that stablize body (input from vestibular system)
output is motor control to musculature except for neck
lateral VSR
input from otolithic organs
modulations from cerebellum via ipsilateral vestibular nuceli
medial VSR
input from SCC
from the contralateral medial vestibular nuclei and the superior and descending vestibular nuclei
Reticulospinal tract
input from all sensory and motor balance systems via vestibular nuclei
vestibulocollic reflexes
acts on muscles in neck to stabilize head in response to velocity detection from otolithic organs
strategies to maintain/restore balance
ankle
hip
stepping
suspensatory
How long after perception of instability do we use strategies to maintain balance
automatic
occur 95-90ms after perception of instability realized
ankle strategy
used when perturbation slow & low amplitude
contact surface firm, wide, longer than foot
muscles recruited distal-proximal (abs then thigh)
head movement in phase with hips
minimal energy
hip strategy
used when perturbation is fast or large amplitude
contact surface unstable or shorter than feet
muscles recruited proximal-distal
head moves out of phase with hips
stepping strategy
used to prevent fall when perturbations are fast or large amplitude
moves BOS to catch up with COG
suspensory strategy
rarely used because lots of energy
forward bend of trunk with hip/knee flexion
may progress to squatting if COG lowered
Cervico-occular reflex
eye movements driven by neck proprioceptors
cervico-spinal reflex
changes in limb position driven by neck afferent activity
cervico-collic reflex
stabilizes head movement in vertical plane
edwalds first law
stimulation of SCC causes eye rotation in plane of canal being stimulated
criteria to maintain binocular fixaiton
- eyes move opposite to head
- eyes rotate in sychnrony with displacement of target in space (i.e., head tilts but image stays horizontal bc eyes are counter rotating to compensate for head tilt)
what amount of retinal slip is enough to reduce visual acuity
2-3 degrees
VOR latency
7ms
frequency range of head movement
0.5-5HZ
frequency range of eyes during VOR
8Hz
frequency of voluntary eye movement
can’t move faster than 1Hz
Angular VOR responsible for
Gaze stabilization
what are used for angular VOR
SCC
Horizontal aVOR causes which muscles to be excited
ipsilateral medial rectus and contralateral rectus
i.e., head rotates R. R medial rectus and L lateral rectus excited.
Vertical AVOR in anterior SCC causes which muscles to be excited
ipsilateral superior rectus and contralateral inferior oblique.
Left anterior canal is stimulated. What way do eyes move and what muscles are stimulated.
Left superior rectus, Right inferior oblique
Eyes move up rotate right
Right anterior canal is stimulated. what way do eyes move and what muscles are stimulated
Right superior rectus and Left inferior oblique
eyes move up and rotate left
Vertical aVOR in posterior SCC causes which muscles to be excited
ipsilateral inferior rectus and contralateral superior oblique
Right posterior canal is stimulated.what way do eyes move and what muscles are excited
Right inferior rectus and Left superior oblique
Eyes move down and left
left posterior canal is stimulated.what way do eyes move and what muscles are excited
Left inferior rectus AND right superior oblique
eyes move down and right
Linear VOR
otholithic organs
angular VOR weakness
responds poorly at less than .1Hz which can interfere with smooth pursuit, OKR and velocity storage mechanism
velocity storage mechanism
allows raw vestibular signals (6-7s decay) to be prolonged so aVOR can transduce sustained head rotation (20s decay)
- happens in neural integrator in brainstem
