Vestibular system Flashcards
what is the location and function of the peripheral receptor apparatus
located in the inner ear
transduction of head motion and position
what is the location and function of the central vestibular nuclei
located in brainstem
integration/distribution of motor and spatial information
what is the function of the vestibulocular network
control of eye movements
what is the function of the vestibulospinal network
coordination of head movements, axial ms and postural reflexes
what is the function of the vestibulothalamocortical network
perception of movement and spatial orientation
where are vestibular receptors found
membranous labyrinth
where is perilymph found
in the space between the bony and membranous labyrinths
where is endolymph found
within the membranous labyrinth
what structure senses rotational head movements
semicircular canals (aka ampulla)
what structure senses translational head movements
otolith organs
what innervates the receptor cells of the vestibular organs
afferent fibers of the vestibular ganglion
what two arteries supply the labyrinth
labyrinthine artery (primary) stylomastoid artery
the labyrinthine artery is a branch of what
AICA
what are the sxs of interrupted blood supply to the labyrinth
vertigo
nystagmus
unstable gait
where are sensory receptors for the semicircular canals found
base of each ampulla
how are receptors in the utricle oriented vs in the saccule
along the base of the utricle
along medial wall of the sacule
what is the ductus reuniens
a duct connecting the saccule to the cochlea
what is the cause of meniere’s dz
disruption of normal endolymph volume => distention of membranous labyrinth
what are the sxs of menieres dz
occurs in unpredictable attacks of: fluctuating hearing loss vertigo positional nystagmus n/v tinnitus
how do you treat menieres dz
diuretic, salt restrictive diet
shunt into endolymphatic sac
what is a kinocilium
a single longer cilia found on a hair cell
how are type I hair cells characterized
chalice shaped
surrounded by nerve calyx
how are type II hair cells characterized
cylindrical
where are the cell bodies that control hair cell sensitivity via vestibular efferents
rostral to vestibular nuclei
lateral to abducens nucleus
what CN activates the cell bodies that control hair cell sensitivity via vestibular efferents
V
how are hair cells organized in the ampulla
embedded in crista
type I in the center
type II in periphery
how are rotational head movement detected
endolymph is displaced => cupula and stereocilia displaced
what is the cupula
gelatinous structure enveloping the ampulla
what is the otolith memrane
a gelatinous coating in the macula which hair cell stereocilia extend into
what is otoconia
calcium carbonate crystals covering the otolith membrane in the macula
what role do otoconia play in sensation of linear acceleration
they are displaced in respose to linear acceleration => bend underlying hair cell stereocilia
where do primary afferents of the vestibular nuclei enter the brainstem
pontomedullary jxn
to what nuclei do afferents from the ampulla project
superior and medial vestibular nuclei
to what nuclei do afferents from the maculae project
lateral, medial and inferior vestibular nuclei
to what nuclei do afferents from the saccule project
contralateral oculomotor nucleus => infulence vertical eye movements
to what cerebellar nuclei do the vestibular nuclei send afferents
dentate and fastigial nuclei
what do vestibulovestibular fibers do
arise from vestibular nuclei and form connections with analogous contralateral nucleus
what do spinovestibular fibers do
arise from all levels of SC => provide proprioceptive input to medial and lateral vestibular nuclei
what does the vestibuloocular reflex do
stabilize eye movements, allowing you to keep fixed gaze when head is moving
vertical eye movements are controlled by what vestibular structures
vertical semicircular canals and saccule
horizontal eye movements are controlled by what vestibular structures
horizontal canals and utricle
torsional eye movements are controlled by what vestibular structures
vertical semicircular canals and utricle
a leftward head turn stimulates the left vestibular nuclei to facilitate contraction of what two muscles
right lateral rectus
left medial rectus
what reflex elicits oppositely directed vertical eye movements when walking or running (to stabilize gaze)
linear vestibuloocular reflex
cold water in the external auditory canal should cause what
nystagmus beating away from ear w/ water
(COWS: cold water/opposite
warm water/same)
in what nuclei are neurons of the lateral vestibulospinal tract
lateral and inferior vestibular nuclei
where do LVST fibers project
to all levels of ipsilateral SC via lateral medulla and anterior funiculus
where do LVST fibers terminate
alpha and gamma motor neurons and interneurons in laminae VII-IX
what is the function of the vestibulospinal network
influence of muscle tone and reflexive postural adjustments
in what nuclei are neurons of the medial vestibulospinal tract
medial vestibular nucleus
lesser from inferior and lateral vestibular nuclei
where do MVST fibers project
bilaterally through medial longitudinal fasciculus of the cervical SC
where do MVST fibers terminate
laminae VII-IX of the cervical SC
what is the function of the MVST
stabilization of the neck (AKA vestibulocolic reflex)
what two areas of the primary somatosensory cortex receive vestibular signals
2v and 3a
what does vestibular stimulation of area 2v do
produce sensation of whole body motion
what does vestibular stimulation of area 3a do
integrate motor control of head and body
what does vestibular stimulation of area 7 of the parietal cortex do
integrate cues of body motion in space (aka spatial awareness)
what does vestibular stimulation of the lateral sulcus and PIVC (parietoinsularvestibular cortex) do
respond to body motion, somatosensory and visual stimuli
what does vestibular stimulation of the prefrontal cortex and superior frontal gyrus do
controls smooth pursuit eye movements and saccades
what is subjective vertigo
pt experiences sensation of spinning while surroundings are not moving
what is objective vertigo
sensation of objects spinning while patient is not moving
-pt will have nystagmus in opposite direction of rotation
what is the most accepted explanation for benign paroxysmal positional vertigo
otoconia become lodged in cupula of semicircular canal (cupulolithiasis)
=> abnormal cupula deflection when head changes postion
where are vestibular schwannomas typically located
cerebellopontine angle
what structures are impinged by a vestibular schwannoma
those traveling in the internal acoustic meatus
- CN VII and VIII
- labyrinthine a
how do patients with a vestibular schwannoma usually present
with hearing loss, tinnitus and unstable gait
what are the sxs of vestibular neuritis
severe vertigo
n/v
no hearing loss/CNS deficits
