vestibular system

Question 1

function of vestibular system

Answer 1

maintain animal’s balance relative to gravity - at rest and during movement

Question 2

two categories of vestibular reflexes

which is faster?

Answer 2

vestibulo-ocular

** vestibulospinal **

Question 3

function of vestibulo-ocular reflexes

Answer 3

stabilize images on the retina

Question 4

clinical signs of vestibulo-ocular reflex damage

Answer 4

nystagmus

Question 5

function of vestibulospinal reflexes

Answer 5

coordinate head and neck movements with rest of body

projections from vestibular nuclei down spinal cord to maintain posture

Question 6

divisions of the vestibulospinal reflexes

Answer 6

lateral and medial tracts

lateral is more important for our current topic

Question 7

middle ear composition

Answer 7

tympanic membrane

auditory ossicles

tympanic cavity

osseous bulla

auditory tube

Question 8

middle ear function

Answer 8

conduct and amplify sound

Question 9

importance of stylomastoid foramen

Answer 9

just caudal to the tympanic bullae

exit of the facial nerve
- large nerve

damage to the vestibular/auditory pathways stimulating pain in that nerve

Question 10

vestibular anatomy

Answer 10

semi-circular canals filled with a semi-circular ducts
- each of the 3 are at right angles to one another

ampullae where the ducts/canals meet the utricle

saccule between utricle/vestibule and cochlear duct

filled with endolymph

Question 11

semi-circular duct function

Answer 11

angular acceleration

rotation of head or body

spinning

Question 12

utriculus and sacculus function

Answer 12

linear acceleration

standstill to running

riding in an elevator

Question 13

5 receptors of the vestibular system

Answer 13

3 ampullae (1 for each of the semi-circular canals)

2 maculae (1 for each the utriculus and sacculus)

Question 14

hair cell function in maculae

Answer 14

multiple sterocilia and 1 kinocilium
- move with the membranous labyrinth

otolithic membrane lags behind

• deflects hair cells
• direction of deflection relative to kinocilium determines if there is hyperpolarization or depolarization

Question 15

crista ampullaris function

Answer 15

receptor of the semi-circular canals (angular acceleration)

hair cells all lined up in one place

head moves
- fluid moves the other direction and pushes the cupula out of place

Question 16

vestibular neural pathway

Answer 16

N1: bipolar neuron

• soma in vestibular ganglion of CN VIII
• axon projects to ipsilateral vestibular nucleus

N2: soma in vestibular nucleus

• ipsilateral and contralateral axons
• project to medial geniculate nucleus
• side branches to CN III, IV, and VI (medial longitudinal fasciculus)

N3: soma in medial geniculate nucleus
- axons to cortex

Question 17

role of cortex in vestibular system

Answer 17

awareness of loss of balance

NOT postural control to maintain balance

Question 18

lateral vestibulospinal tract pathway

Answer 18

axons from ipsilateral vestibular nuclei

no decussation

projects to alpha motor neurons in spinal cord

Question 19

lateral vestibulospinal tract function

Answer 19

facilitates ipsilateral extensor muscles and inhibits flexor muscles

some contralateral activity (opposite of above)

Question 20

lateral vestibulospinal tract damage

Answer 20

results in lack of sufficient extension on ipsilateral side and therefore leaning toward that side

Question 21

medial vestibulospinal tract pathway

Answer 21

axons from vestibular nuclei

ipsilateral in ventral funiculus of cervical and cranial thoracic spinal cord

innervates neck muscles

Question 22

vestibular / cerebellar connection

Answer 22

ipsilateral caudal peduncle

flocculonodular lobe

Question 23

peripheral vestibular disease affects….

Answer 23

receptors

labyrinth

vestibulocochlear nerve

Question 24

central vestibular disease affects…

Answer 24

vestibular nuclei

flocculonodular lobe / caudal peduncle

vestibulospinal/vestibulo-ocular pathways

Question 25

clinical signs of vestibular dysfunction

Answer 25

nystagmus

head tilt

tight circling

strabismus

ataxia

vomiting, salivation
- interpreted as nausea

Question 26

defining nystagmus

Answer 26

1. direction
2. head position
3. eye coordination

Question 27

naming head tilts

Answer 27

named for most ventral side

Question 28

circling but no head tilt?

Answer 28

likely not vestibular disease

Question 29

patient head is tilted right and is circling tightly to the right. the lesion is likely on the…?

Answer 29

right

Question 30

stabismus is ____ to the vestibular dysfunction

Answer 30

ipsilateral

Question 31

direction of vestibular strabismus

Answer 31

ventral or ventrolateral

Question 32

peripheral versus central vestibular disease

Answer 32

clinical signs of central disease can mimic those of peripheral - look for specific central signs…

vertical nystagmus
- positional, dysconjugate

asymmetrical ataxia without weakness

altered mentation

other CN deficits

long tract signs

• ipsilateral
• both TL and PL

ipsilateral cerebellar signs (hypermetria, intention tremor, absent menace)

Question 33

paradoxical vestibular disease

Answer 33

signs are opposite of the lesion

• nystagmus toward lesion
• head tilt away from lesion

look for brainstem and cerebellar deficits (truely ipsilateral)

• CN V
• CN VII
• CPs

indicates disease of the caudal cerebellar peduncle, flocculonodular lobe, rostral and medial vestibular nuclei