Vestibular system Flashcards
The five components of the Vestibular system: Peripheral receptor apparatus
in the inner ear, responsible for transducing head motion/position
The five components of the Vestibular system: Central vestibular nuclei
brainstem - integrating and distributing info that controls motor activities and spacial orientation
The five components of the Vestibular system: Vestibuloocular network
coordinates head movements, axial musculature and postural reflexes
The five components of the Vestibular system: Vestibulothalamocortical network
conscious perception of movement/ spatial orientation
What are the Vestibular receptor organs and their functions
Semicircular canals (anterior, posterior, horizontal): rotational head movements (angular accelerations)
Otolith organs of the utricle and saccule: for transitional head movements (linear accelerations) (saccule = verticle, utricle = horizontal)
they relay the information to the ipsilateral vestibular ganglion
What is the blood supply to the labyrinth organ
Labyrinthine artery which is a branch of the basilar A
also recieves blood supply from the stylomastoid artery but is not the main blood supply
Menieres disease
Distruption in the normal endolymph volume leading to endolymphatic hydrops (an abnormal distention of the membranous labyrinth)
symptoms: vertigo, fluctuating hearing, vestibular symptoms like tinnitys vomiting and inabillity to make head movements
Treatment:
Diuretic and salt restricted diet to reduce hydrops
implantation of a small shunt into the swollen endolymphatic sac
What are the 2 types of hair cells and what are their function
Type I and II hair cells
difference is type 1 cell has nerve calyx and type II has boutons
movement of the sterocilia away from the kinocilium will hyperpolarize the cell and not send an AP
movement of the sterocilla towards the kinocilium will depolarize the cell and send an AP
The Ampullae
located in the semicircular ducts
hair cells found in the cristae and all face the same way nd extend up into the cupula
during rottional acceleration the endolymph will bend the cupula and displace the sterocilia away or towards the kinocilia
The Maculae
Utricle and saccule
sterocillia extend into the gelatinous otolith membrane covered by the otoconia
gravity and linear acceleration move the otoconia which will move the sterocilia away or toward the kinocilia
What does the secondary neurons in the vestibular nuclei travel to, and in what tracts
travel to the CN III, IV, VI
vestibulocerebellum, SC, reticular formation, and the thalamus
Vestibulovestibular fibers
reciprocal connections with analogous contralateral nucleus
Spinovestibular fibers
arise from all SC levels to provide proprioceptive input
Vestibulocerebellar fibers
fibers course through the juxtarestiform body which is part of the inferior cerebellar peduncle
- Primary vestibulocerebellar fibers target the dentate nucleus and terminate as mossy fibers
- secondary vestibuocerebellar fibers target the flocculonodular love and fastigal and dentate nucleus
Reciprocal cerebellovestibular fibers from the fastigal nucleus can send info back via the juxtarestiform body to provide info for regulatory mechanisims, control of eye movements, head movements, and posture
Dizziness
Nonspecific term that generally means a spatial disorientation
- may or may not involve feelings of movement
- may be accompanied by nausea or postural instability
- not exclusively vestibular in orgin
Vertigo, and the two types
an illusion of body motion, often spinning or turning, experienced when no real motion is taking place
subject vertigo: the paitent experiences sensation of spinning while things in the environment are not moving
objective vertigo: the sensation is one of objects spinning while patient is not moving
Benign Paraxysmal positional vertigo
one of the most common vestibular disorder
brief episodes of vertigo that coincide with particular changes in body position
triggered by turning over in bed, getting up in the morning, bending over or rising from a bent position
otoconial crystals from the utricle seperate from the otolith membrane and become lodged in the cupula of a semicircular canal (cupulolithiasis)
-produces abnormal cupula deflections when the head changes position relative to gravity
Vestibular schwannona
Benign tumor that originates from the schwann cells of the vestibular root
typically within cerebellopontine angle and impinges n structures traversing the internal acoustic meatus (CN VII, VIII, labyrinthine artery)
slow growing, hearing loss, gait difficulties, tinnitus
Vestibular neuritis
severe vertigo, nausea, vomitting, but no hearing loss or other CNS defects
edema of the vestibular nerve
-acute viral infection such as herpes simplex virus
history of URI, cold, influenza
treatments: antiemetics, vestibular supressants, corticosteroids, and antiviral agents
Lateral Vestibulospinal tract
projects to ipsilateral SC and controls extensors in the limbs for maintenance of posture
- anterorostral area is the cervical cord
- posterocaudal region is the lumbosacral cord
Medial Vestibulospinal tract
carry input from vestibular receptors, cerebellum and PCMLS
descend bilaterally and terminate in the cervical SC and stabilize the neck flexor and extensor musculature
critical in the vestibulocolic reflex which stabilizes the head via activation of the neck musculature
what are the cortical and thalamic projections done via the the vestibular nuclei
thalamus: Ventral posterior nuclear complex
cortex:
Primary samatosensory cortex
Parietoinsular vestibular cortex: lesions cause vertigo and loss of visual vertical
Posterior parietal cortex: lesions result in confusion and in spatial awareness
Vestibuloocular reflux
stabilizes the retinal images during head movements through vestibular input
head rotations stimulate semicircular canals which provide the vestibular input about head motion and drives counter rotation of the eyes
need: activation of ocular muscles for slow phase
activation: vestibular apparatus
effectors: lateral and medial rectus
slowphase: counters the head movement
fast phase: movement that resets the eyes
nystagmus
combo of the slow phase puncuated by a fast return phase
if the line of sight is fixed:
the head will turn and the slow phase will move the opposite way
then once the eyes reach the edge of the orbit they snap back to center via the way the head was turning (this direction is the name of the nystagmus)
How does the semicircular canals, and musces activate during VOR
whichever way the head is rotating, the semicircular duct on that side of the head that is turning will activate and the other side will deactivate
-then those activation neurons will synapse the Vestibular nuclei, which will synapse the contralateral abducens (lateral rectus) and the ipsilateral oculomotor (medial rectus)
causes eyes to move slowly the opposite way of the head rotation
Spontaneous Nystagmus
Unilateral damage to vestibular system
silencing of output from damage side which means there is net differences in firing rates of CN VIII when head is stationary
(the intact side will fire)
have difficulty maintaining fixation
damage could be both peripheral and central damage to brainstem or cerebellar structures
Caloric test
uses water to alter convection in endolymph currents and cause CNVIII firing
warm water makes a nystagmus towards the ear recieving the water
cold water makes a nystagmus away from the ear recieving the cold water
Oculocephalic reflex
rotating the head back and forth horizontally induces compensatory eye movements that are dependent on visual and vestibular function
if this reflex is broken or brainstem lesion = dolls eyes, the eyes will move with the head movements
if their is an intact brainsterm the patients eyes will remain looking forward always and not show dolls eyes
