Vestibular System

Question 1

what are the main functions of the vestibular system?

Answer 1

knowing which way is up and how you’re moving through space

*rapid estimate of head motion

Question 2

where are the vestibular organs located?

Answer 2

in the inner ear

Question 3

what is the vestibular labyrinth composed of?

Answer 3

an outer boney labyrinth filled with perilymph and a inner membranous layer filled with endolymph

Question 4

what does the inner membraneous layer contain that translates head movements into electrical impulses ?

Answer 4

utricle, saccule and ampullae

Question 5

what are vestibular hair cells?

Answer 5

specialized cells that synapse with neurons from the vestibular ganglion

Question 6

vestibular hair cells are tonically active which means what?

Answer 6

vestibular neurons receive constant baseline stimulation

Question 7

what do the utricle and saccule detect and in what direction?

Answer 7

• linear acceleration: movement in a straight line
• static head tilt

utricle detects horizontal movements
saccule detects vertical movements

Question 8

linear acceleration is detected by what structure in the utricle or saccule?

Answer 8

macula

Question 9

why is the different orientation of hair cells important?

Answer 9

any given head movement will maximally depolarize one group of hair cells while maximally inhibiting a complementary set of hair cells

Question 10

the ampullae of the semicircular ducts detects what type of motion?

Answer 10

rotational movement (angular acceleration)

Question 11

what are the detectors inside the ampulla called?

Answer 11

cristae

Question 12

each semicircular duct contains an ampulla filled with what?

Answer 12

endolymph and hair cells that synapse with vestibular afferents

Question 13

hair cells have stereocilia that extend into what?

Answer 13

gelatinous layer called cupula

Question 14

when turning your head to the left what is the vestibular response?

Answer 14

• cristae move but fluid lags behind creating a flow in the opposite direction
• hair cells in the left ampulla are depolarized as the cupula bends towards the utricle
• the hair cells in the right ampulla are hyperpolarized as the cupula is bent away from the utricle
• leads to enhanced excitation in the left vestibular nerve

Question 15

central projections from the vestibular ganglia combine and become portions of what CN?

Answer 15

VIII

Question 16

CN VIII travels through what and enters the brainstem where?

Answer 16

internal acoustic meatus
pontomedullary junction

Question 17

where do the processes of the vestibular ganglion synapse and then where do most travel?

Answer 17

neurons of the vestibular nuclei
travel through cerebellar peduncle to synapse on neurons of the cerebral cortex/the VP complex of the thalamus

Question 18

where do the projections from the neurons of the vestibular nuclei travel to?

Answer 18

• cortical regions to provide awareness of head position
• spinal cord for vestibulospinal tract
• cerebellum for posture and balance
• cranial nerve nuclei of extraocular muscles (III, IV, VI)

Question 19

where are the 4 vestibular nuclei located?

Answer 19

floor of the 4th ventricle of the pons and rostral medulla

Question 20

what is the parieto-insular vestibular cortex?

Answer 20

key region in processing vestibular information

Question 21

what is the vestibulo-ocular reflex?

Answer 21

stabilizes eye position to keep eyes focused on an object of interest as the head moves

Question 22

what is nystagmus?

Answer 22

During sustained rotation, the eyes will eventually reach the end of their orbit. When they can no longer move in that direction, they will reset via a saccade to a central position

Question 23

what is saccade?

Answer 23

a rapid simultaneous movement of both eyes between two points

Question 24

the fast resetting movements of nystagmus are driven by what area?

Answer 24

paramedian pontine reticular formation in the tegmentum of the pons

Question 25

the movements of saccade are mediated by input from what CN?

Answer 25

CN VIII

Question 26

what does damage to the vestibular system cause?

Answer 26

postural instability, vertigo and spontaneous nystagmus

Question 27

what is vertigo?

Answer 27

spinning or whirling sensation: illusion of movement of self or the world

Question 28

what is benign paroxysmal positional vertigo and what is it caused by (BPPV)?

Answer 28

positional vertigo that lasts for a few seconds after change in position

caused by loose otoconia

Question 29

what is the treatment for BPPV?

Answer 29

epley maneuver