vestibular function

Question 1

what is the vestibular system?

Answer 1

A sensory system essential in the control of posture and balance.

Question 2

where is the vestibular system found?

Answer 2

the inner ear

Question 3

what is the vestibular system composed of?

Answer 3

3 semi circular canals
utricle to which the semi circular canals connect
saccule

Question 4

what are the utricle and the saccule collectively known as?

Answer 4

otolith organs

Question 5

what is the function of the otolith organs?

Answer 5

they detect linear acceleration and encode information about the position of the head in the space?

Question 6

what is the function of the utricle?

Answer 6

back/front head tilt

Question 7

what is the function of the saccule?

Answer 7

detects vertical movement of the head

Question 8

what is the function of the semi circular canals?

Answer 8

to detect rotational acceleration

Question 9

where are the sensory cells of the semi circular canals located>

Answer 9

swellings in the base of the bony canals called ampulla

Question 10

what is contained within the ampulla?

Answer 10

snesory receptors called cristae

Question 11

what are cristae composed of?

Answer 11

cupula

Question 12

what does the cupula respond to?

Answer 12

movement of the endolymph fluid within the canals

Question 13

what is embedded within the cupula?

Answer 13

cilia of hair cells which synapse directly with the sensory neurons of the vestibular nerve

Question 14

what do the hair cells detect?

Answer 14

rotational acceleration

Question 15

what are the two types of cilia of hair cells?

Answer 15

single, large kinocilium

set of progessively smaller stereocilia

Question 16

what causes an increased discharge of APs in the vestibular nerve?

Answer 16

distortion of the cilia in the direction of the kinocilium

Question 17

what causes a decreased discharge of APs in the vestibular nerve?

Answer 17

distortion of cilia away from the kinocilium

Question 18

what is the name for the sensory apparatus of the utricle and saccule?

Answer 18

maculae

Question 19

what directions are the maculae orientated in each of the otolith organs?

Answer 19

utricle - horizontal place

saccule - vertical plane

Question 20

where do the cilia of the maccule protrude into?

Answer 20

otolith membrane

Question 21

what is embedded in the otolith membrane?

Answer 21

CaCO3 crystals called otoliths

Question 22

where do projections from the vestibular nuclei project to?

Answer 22

ipsilaterally, bilaterally and contra laterally to descending motor pathways

Question 23

how do vestibular nuclei project to the cerebral cortex?

Answer 23

via the thalamus

Question 24

what is kinaesthesia?

Answer 24

perception of movement and body position

Question 25

what is the function of the tonic labyrinthine reflexes?

Answer 25

keep the axis of the head in a constant relationship with the rest of the body

Question 26

what do the tonic labyrinthine reflexes use information from?

Answer 26

the maculae and neck proprioceptors

Question 27

what is the function of dynamic righting reflexes?

Answer 27

rapid postural adjustments that are made to stop you falling when you trip

Question 28

what happens if someone who has dysfunctional vestibular apparatus closes their eyes?

Answer 28

balance is immediately lost (reduced vestibulo ocular reflexes)

Question 29

what is the static vestibulo-ocular reflex?

Answer 29

when you tilt your head, the eyes intort/extort to compensate, so that over a certain range, the image stays the right way up

Question 30

what is dynamic vestibular nystagmus?

Answer 30

a series of saccadic eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite the head rotating

Question 31

in dynamic vestibular nystagmus, what happens when the eyeball comes to the end of its range of movement?

Answer 31

rapidly flicks back to the zero position (straight ahead)

Question 32

what is post rotatory nystagmus?

Answer 32

subjects are rotated in a barany chair, if they are rotated to the left, there is left nystagmus. at the end of rotation for about 20 seconds, during deceleration they get a right nystagmus

Question 33

why do subjects get nystagmus to the opposite side of acceleration at the end of a post rotatory nystagmus test?

Answer 33

endolymph has "caught up" and pushes the cupula to the opposite direction

Question 34

what is caloric stimulation used to test?

Answer 34

horizontal SSC

Question 35

what is caloric stimulation?

Answer 35

When the outer ear is washed with either cold or warm fluid, the temperature difference from core 37C, gets through the thin bone and sets up convection currents which affect the endolymph. Warm fluid (44C) causes nystagmus towards affected side, cold (30C) causes nystagmus away from affected side (COWS – Cold Opposite, Warm Same).

Question 36

what is the medical term for motion sickness?

Answer 36

kinetosis

Question 37

what can cause kinetosis?

Answer 37

powerful maintained stimulation of the vestibular system

Question 38

what is vertigo?

Answer 38

the perception of movement in the absence of movement

Question 39

what can lead to nystagmus at rest?

Answer 39

lesions of the brainstem

Question 40

what are symptoms of menieres disease?

Answer 40

vertigo nausea nystagmus tinnitus

Question 41

what is menieres disease associated with?

Answer 41

over production of endolymph causing increased pressure

Question 42

what is labyrinthitis?

Answer 42

acute interference with normal vestibular function as a result of infection