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Flashcards in vestibular system Deck (33)
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1

function of vestibular system

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

2

two categories of vestibular reflexes

which is faster?

vestibulo-ocular

** vestibulospinal **

3

function of vestibulo-ocular reflexes

stabilize images on the retina

4

clinical signs of vestibulo-ocular reflex damage

nystagmus

5

function of vestibulospinal reflexes

coordinate head and neck movements with rest of body

projections from vestibular nuclei down spinal cord to maintain posture

6

divisions of the vestibulospinal reflexes

lateral and medial tracts

lateral is more important for our current topic

7

middle ear composition

tympanic membrane

auditory ossicles

tympanic cavity

osseous bulla

auditory tube

8

middle ear function

conduct and amplify sound

9

importance of stylomastoid foramen

just caudal to the tympanic bullae

exit of the facial nerve
- large nerve

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

10

vestibular anatomy

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

11

semi-circular duct function

angular acceleration

rotation of head or body

spinning

12

utriculus and sacculus function

linear acceleration

standstill to running

riding in an elevator

13

5 receptors of the vestibular system

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

2 maculae (1 for each the utriculus and sacculus)

14

hair cell function in maculae

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

15

crista ampullaris function

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

16

vestibular neural pathway

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

17

role of cortex in vestibular system

awareness of loss of balance

NOT postural control to maintain balance

18

lateral vestibulospinal tract pathway

axons from ipsilateral vestibular nuclei

no decussation

projects to alpha motor neurons in spinal cord

19

lateral vestibulospinal tract function

facilitates ipsilateral extensor muscles and inhibits flexor muscles

some contralateral activity (opposite of above)

20

lateral vestibulospinal tract damage

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

21

medial vestibulospinal tract pathway

axons from vestibular nuclei

ipsilateral in ventral funiculus of cervical and cranial thoracic spinal cord

innervates neck muscles

22

vestibular / cerebellar connection

ipsilateral caudal peduncle

flocculonodular lobe

23

peripheral vestibular disease affects....

receptors

labyrinth

vestibulocochlear nerve

24

central vestibular disease affects...

vestibular nuclei

flocculonodular lobe / caudal peduncle

vestibulospinal/vestibulo-ocular pathways

25

clinical signs of vestibular dysfunction

nystagmus

head tilt

tight circling

strabismus

ataxia

vomiting, salivation
- interpreted as nausea

26

defining nystagmus

1. direction

2. head position

3. eye coordination

27

naming head tilts

named for most ventral side

28

circling but no head tilt?

likely not vestibular disease

29

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

right

30

stabismus is ____ to the vestibular dysfunction

ipsilateral

31

direction of vestibular strabismus

ventral or ventrolateral

32

peripheral versus central vestibular disease

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)

33

paradoxical vestibular disease

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