Vestibular System Flashcards
what are the main functions of the vestibular system?
knowing which way is up and how you’re moving through space
*rapid estimate of head motion
where are the vestibular organs located?
in the inner ear
what is the vestibular labyrinth composed of?
an outer boney labyrinth filled with perilymph and a inner membranous layer filled with endolymph
what does the inner membraneous layer contain that translates head movements into electrical impulses ?
utricle, saccule and ampullae
what are vestibular hair cells?
specialized cells that synapse with neurons from the vestibular ganglion
vestibular hair cells are tonically active which means what?
vestibular neurons receive constant baseline stimulation
what do the utricle and saccule detect and in what direction?
- linear acceleration: movement in a straight line
- static head tilt
utricle detects horizontal movements
saccule detects vertical movements
linear acceleration is detected by what structure in the utricle or saccule?
macula
why is the different orientation of hair cells important?
any given head movement will maximally depolarize one group of hair cells while maximally inhibiting a complementary set of hair cells
the ampullae of the semicircular ducts detects what type of motion?
rotational movement (angular acceleration)
what are the detectors inside the ampulla called?
cristae
each semicircular duct contains an ampulla filled with what?
endolymph and hair cells that synapse with vestibular afferents
hair cells have stereocilia that extend into what?
- gelatinous layer called cupula for the ampulla
- gelatinous membrane called the otolithic membrane for utricle/saccule
when turning your head to the left what is the vestibular response?
- 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
central projections from the vestibular ganglia combine and become portions of what CN?
VIII
CN VIII travels through what and enters the brainstem where?
internal acoustic meatus
pontomedullary junction
where do the processes of the vestibular ganglion synapse and then where do most travel?
neurons of the vestibular nuclei
travel through cerebellar peduncle to synapse on neurons of the cerebral cortex/the VP complex of the thalamus for awareness of head position
where do the projections from the neurons of the vestibular nuclei travel to?
- 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)
where are the 4 vestibular nuclei located?
floor of the 4th ventricle of the pons and rostral medulla
what is the parieto-insular vestibular cortex?
key region in processing vestibular information
what is the vestibulo-ocular reflex?
stabilizes eye position to keep eyes focused on an object of interest as the head moves
what is nystagmus?
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
what is saccade?
a rapid simultaneous movement of both eyes between two points
the fast resetting movements of nystagmus are driven by what area?
paramedian pontine reticular formation in the tegmentum of the pons
the movements of saccade are mediated by input from what CN?
CN VIII
what does damage to the vestibular system cause?
postural instability, vertigo and spontaneous nystagmus
what is vertigo?
spinning or whirling sensation: illusion of movement of self or the world
what is benign paroxysmal positional vertigo and what is it caused by (BPPV)?
positional vertigo that lasts for a few seconds after change in position
caused by loose otoconia
what is the treatment for BPPV?
epley maneuver
