vestibular system

Question 1

what happens to body mass when an animal turns its head to the right?

Answer 1

body mass shifts to the right side

Question 2

why must vestibular signals reach the spinal cord?

Answer 2

to support shifted body mass and maintain posture

Question 3

what effect do vestibular nuclei have on ipsilateral limbs?

Answer 3

stimulate extensor muscles and inhibit flexor muscles

Question 4

what effect do vestibular nuclei have on contralateral limbs?

Answer 4

inhibit extensor muscles and facilitate flexor muscles

Question 5

what spinal tract mediates vestibular control of posture?

Answer 5

vestibulospinal pathways

Question 6

why do vestibular nuclei project to the cerebellum?

Answer 6

to convey head position and movement information

Question 7

what additional information does the cerebellum integrate?

Answer 7

proprioceptive input from the body

Question 8

what is the cerebellum’s role in vestibular function?

Answer 8

co-ordination of motor output, posture and balance

Question 9

why must eye position adjust when the head moves?

Answer 9

to maintain useful visual input

Question 10

which cranial nerves control eye movements?

Answer 10

CN III, IV and VI

Question 11

what reflex maintains vision during head movement?

Answer 11

physiological nystagmus

Question 12

describe the slow phase of physiological nystagmus

Answer 12

slow drift of the eyes relative to the head

Question 13

describe the fast phase of physiological nystagmus?

Answer 13

quick corrective jerk in the direction of movement

Question 14

what brainstem centre also receives vestibular input?

Answer 14

the vomiting centre

Question 15

what causes motion sickness?

Answer 15

mismatch between vestibular and visual inputs

Question 16

why do vestibular nuclei project to the cerebrum?

Answer 16

for conscious perception of head movement

Question 17

what is vestibular disease?

Answer 17

a collection of clinical signs due to vestibular dysfunction

Question 18

why is vestibular disease considered a syndrome?

Answer 18

it has many possible causes

Question 19

list possible lesion locations in vestibular disease

Answer 19

• inner ear
• CN VII
• vestibular nuclei

Question 20

what happens to vestibular nerve firing on the lesion side?

Answer 20

decreased action potential firing

Question 21

how does the brain interpret unequal vestibular input?

Answer 21

as head movement toward the intact side

Question 22

in a right-sided lesion, which way does the animal tilt?

Answer 22

toward the right (side of the lesion)

Question 23

why does head tilt usually point toward the lesion?

Answer 23

due to altered extensor muscle activation

Question 24

what causes ataxia in vestibular disease?

Answer 24

poor co-ordination of posture and movement

Question 25

how does ataxia typically present?

Answer 25

- broad-based stance - swaying - falling

Question 26

in unilateral disease, which side does the animal fall toward?

Answer 26

usually the side of the lesion

Question 27

what is vestibular nystagmus?

Answer 27

involuntary rhythmic eye movements

Question 28

which direction is the slow phase of nystagmus?

Answer 28

toward the side of the lesion

Question 29

which direction is the fast phase of nystagmus?

Answer 29

away from the lesion (direction of perceived movement)

Question 30

what is strabismus in vestibular disease?

Answer 30

abnormal eye position

Question 31

when is vestibular strabismus often visible?

Answer 31

in certain head positions

Question 32

what structures make up the peripheral vestibular system?

Answer 32

vestibular apparatus and CN VIII

Question 33

what structures make up the central vestibular system?

Answer 33

vestibular nuclei and their CNS projections

Question 34

which signs suggest central vestibular disease?

Answer 34

- postural deficits - altered mentation - multiple CN signs - vertical nystagmus

Question 35

what features support idiopathic peripheral vestibular disease?

Answer 35

- head tilt - horizontal nystagmus - normal mentation - no other CN deficits - spontaneous improvement