Vestibular system

Question 1

The five components of the Vestibular system: Peripheral receptor apparatus

Answer 1

in the inner ear, responsible for transducing head motion/position

Question 2

The five components of the Vestibular system: Central vestibular nuclei

Answer 2

brainstem - integrating and distributing info that controls motor activities and spacial orientation

Question 3

The five components of the Vestibular system: Vestibuloocular network

Answer 3

coordinates head movements, axial musculature and postural reflexes

Question 4

The five components of the Vestibular system: Vestibulothalamocortical network

Answer 4

conscious perception of movement/ spatial orientation

Question 5

What are the Vestibular receptor organs and their functions

Answer 5

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

Question 6

What is the blood supply to the labyrinth organ

Answer 6

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

Question 7

Menieres disease

Answer 7

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

Question 8

What are the 2 types of hair cells and what are their function

Answer 8

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

Question 9

The Ampullae

Answer 9

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

Question 10

The Maculae

Answer 10

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

Question 11

What does the secondary neurons in the vestibular nuclei travel to, and in what tracts

Answer 11

travel to the CN III, IV, VI

vestibulocerebellum, SC, reticular formation, and the thalamus

Question 12

Vestibulovestibular fibers

Answer 12

reciprocal connections with analogous contralateral nucleus

Question 13

Spinovestibular fibers

Answer 13

arise from all SC levels to provide proprioceptive input

Question 14

Vestibulocerebellar fibers

Answer 14

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

Question 15

Dizziness

Answer 15

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

Question 16

Vertigo, and the two types

Answer 16

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

Question 17

Benign Paraxysmal positional vertigo

Answer 17

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

Question 18

Vestibular schwannona

Answer 18

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

Question 19

Vestibular neuritis

Answer 19

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

Question 20

Lateral Vestibulospinal tract

Answer 20

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

Question 21

Medial Vestibulospinal tract

Answer 21

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

Question 22

what are the cortical and thalamic projections done via the the vestibular nuclei

Answer 22

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

Question 23

Vestibuloocular reflux

Answer 23

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

Question 24

nystagmus

Answer 24

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)

Question 25

How does the semicircular canals, and musces activate during VOR

Answer 25

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

Question 26

Spontaneous Nystagmus

Answer 26

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

Question 27

Caloric test

Answer 27

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

Question 28

Oculocephalic reflex

Answer 28

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