part 5

Question 1

what does the vestibulopsinal tract do

Answer 1

controls postural orientation
- collaborates with reflexes elicited by stimulation of the vestibular and visual reflexes

Question 2

what are the components of the vestibulospinal tract

Answer 2

vestibulospinal reflex
vestibulocolic reflex

Question 2

what does the VSR do

Answer 2

gathers static and dynamic reflexes that stablize body (input from vestibular system)
output is motor control to musculature except for neck

Question 3

lateral VSR

Answer 3

input from otolithic organs
modulations from cerebellum via ipsilateral vestibular nuceli

Question 4

medial VSR

Answer 4

input from SCC
from the contralateral medial vestibular nuclei and the superior and descending vestibular nuclei

Question 5

Reticulospinal tract

Answer 5

input from all sensory and motor balance systems via vestibular nuclei

Question 6

vestibulocollic reflexes

Answer 6

acts on muscles in neck to stabilize head in response to velocity detection from otolithic organs

Question 7

strategies to maintain/restore balance

Answer 7

ankle
hip
stepping
suspensatory

Question 8

How long after perception of instability do we use strategies to maintain balance

Answer 8

automatic
occur 95-90ms after perception of instability realized

Question 9

ankle strategy

Answer 9

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

Question 10

hip strategy

Answer 10

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

Question 11

stepping strategy

Answer 11

used to prevent fall when perturbations are fast or large amplitude
moves BOS to catch up with COG

Question 12

suspensory strategy

Answer 12

rarely used because lots of energy
forward bend of trunk with hip/knee flexion
may progress to squatting if COG lowered

Question 13

Cervico-occular reflex

Answer 13

eye movements driven by neck proprioceptors

Question 14

cervico-spinal reflex

Answer 14

changes in limb position driven by neck afferent activity

Question 15

cervico-collic reflex

Answer 15

stabilizes head movement in vertical plane

Question 16

edwalds first law

Answer 16

stimulation of SCC causes eye rotation in plane of canal being stimulated

Question 17

criteria to maintain binocular fixaiton

Answer 17

1. eyes move opposite to head
2. 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)

Question 18

what amount of retinal slip is enough to reduce visual acuity

Answer 18

2-3 degrees

Question 19

VOR latency

Answer 19

7ms

Question 20

frequency range of head movement

Answer 20

0.5-5HZ

Question 21

frequency range of eyes during VOR

Answer 21

8Hz

Question 22

frequency of voluntary eye movement

Answer 22

can’t move faster than 1Hz

Question 23

Angular VOR responsible for

Answer 23

Gaze stabilization

Question 24

what are used for angular VOR

Answer 24

SCC

Question 25

Horizontal aVOR causes which muscles to be excited

Answer 25

ipsilateral medial rectus and contralateral rectus i.e., head rotates R. R medial rectus and L lateral rectus excited.

Question 26

Vertical AVOR in anterior SCC causes which muscles to be excited

Answer 26

ipsilateral superior rectus and contralateral inferior oblique.

Question 27

Left anterior canal is stimulated. What way do eyes move and what muscles are stimulated.

Answer 27

Left superior rectus, Right inferior oblique Eyes move up rotate right

Question 28

Right anterior canal is stimulated. what way do eyes move and what muscles are stimulated

Answer 28

Right superior rectus and Left inferior oblique eyes move up and rotate left

Question 29

Vertical aVOR in posterior SCC causes which muscles to be excited

Answer 29

ipsilateral inferior rectus and contralateral superior oblique

Question 30

Right posterior canal is stimulated.what way do eyes move and what muscles are excited

Answer 30

Right inferior rectus and Left superior oblique Eyes move down and left

Question 31

left posterior canal is stimulated.what way do eyes move and what muscles are excited

Answer 31

Left inferior rectus AND right superior oblique eyes move down and right

Question 32

Linear VOR

Answer 32

otholithic organs

Question 33

angular VOR weakness

Answer 33

responds poorly at less than .1Hz which can interfere with smooth pursuit, OKR and velocity storage mechanism

Question 34

velocity storage mechanism

Answer 34

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