Vestibular System

Question 1

Where is the peripheral receptor apparatus found and what does it do?

Answer 1

Found in inner ear; responsible for transducing head motion/position

Question 2

Where is the central vestibular nuclei found and what does it do?

Answer 2

Brainstem; inegrating and distributing info that controls motor activities and spatial orientation

Question 3

Where is the vestibuloocular network found and what does it do?

Answer 3

Found in vestibular nuclei; involved in the control of eye movements

Question 4

What does the vestibulospinal network do?

Answer 4

Coordinates head movements, axial musculature, and postural reflexes

Question 5

What does the vestibulothalamocortical network do?

Answer 5

Conscious perception of movement/spatial orientation

Question 6

What are semicircular canals?

Answer 6

Function in horizontal, anterior, posterior rotational head movements (angular accelerations)

Question 7

What are otolith organs of utricle and saccule?

Answer 7

Function in translational head movements (linear accelerations)

Question 8

What are receptor cells in vestibular organs innervated by?

Answer 8

Primary afferent fibers of vestibular ganglion (Scarpa ganglion)

Question 9

Where do the central processes of the bipolar cells travel and terminate?

Answer 9

Enter brainstem and terminate in ipsilateral vestibular nuclei and cerebellum

Question 10

What is perilymph? What is endolymph?

Answer 10

Peri: located between membranous and bony labyrinths; similar to CSF

Endo: located within membranous labyrinth; bathes receptors of auditory and vestibular systems

Question 11

What maintains the different ion concentrations in the peri and endolymph?

Answer 11

Maintained by secretory cells in membranous labyrinth and endolymphatic sac

Question 12

What causes vestibular disease?

Answer 12

Disturbances in volume or ionic content of endolymph

Question 13

What supplies blood to the labyrinth?

Answer 13

Labyrinthine artery, a branch of the AICA; enters temporal bone via internal auditory meatus

Stylomastoid artery also feeds semicircular canals but is not their primary source

Question 14

What happens when you interrupt blood supply to the labyrinth?

Answer 14

Vertigo, nystagmus, and/or unstable gait due to a compromised vestibular and cochlear function

Question 15

What is Meniere’s Disease?

Answer 15

Disruption of normal endolymph volume, resulting in endolymphatic hydrops (abnormal distention of membranous labyrinth)

Question 16

What are the symptoms of Meniere’s?

Answer 16

Fluctuating hearing loss, vertigo, positional nystagmus, and nausea; also unpredictable attacks of auditory and vestibular symptoms, including vomiting, tinnitus, and inability to make head movements or even stand passively

Question 17

What are the treatments for Meniere’s?

Answer 17

Diuretic and salt restricted diet to reduce hydrops; implantation of a small shunt into swollen endolymphatic sac

Question 18

Describe hair cells (type 1 and 2)

Answer 18

Contain 60-100 stereocilia and single kinocilium; CN VIII innervation; movement of stereocilia towards or away from kinocilium will de- or hyperpolarize the cell

Bundled in vestibular organs with specific orientations, responsive various head displacements

Question 19

What is the ampullae?

Answer 19

Semicircular ducts; hair cells embedded in cristae, extends across the base of ampulla and extend into cupula; function in rotational/angular accelerations -> displaces endolymph -> bends cupula to one side or other -> displaces stereocilia

Question 20

What is the maculae?

Answer 20

Found in utricle and saccule; stereocilia extend into gelatinous otolith membrane covered by otoconia; function in gravity/linear accelerations -> displace otoconia -> bend underlying hair cell stereocilia

Question 21

What are vestibulovestibular fibers?

Answer 21

Reciprocal connections w/ analogous contralateral nucleus

Question 22

What are spinovestibular fibers?

Answer 22

Arise from all SC levels to provide proprioceptive input

Question 23

What do primary vestibulocerebellar fibers do?

Answer 23

Target dentate nucleus and terminate as mossy fibers

Question 24

What do secondary vestibulocerebellar fibers do?

Answer 24

Target flocculonodular lobe and fastigial and dentate nuclei

Question 25

What do cerebellovestibular fibers do?

Answer 25

Target vestibular nuclei and provide regulatory mechanisms for control of eye movements, head movements, and posture

Question 26

What is dizziness?

Answer 26

Nonspecific term that generally means a spatial disorientation; may/may not involve feelings of movement; may be accompanied by nausea or postural instability; not exclusively vestibular in origin

Question 27

What is vertigo? Subjective vertigo? Objective vertigo?

Answer 27

Vertigo: illusion of body motion, often spinning or turning, experienced when no real motion is taking place Subjective: patient experiences the sensation of spinning while things in the environment are not moving Objective: sensation is one of objects spinning while patient is not moving

Question 28

What is benign paroxysomal positional vertigo?

Answer 28

Characterized by 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 bent position

Question 29

What is a vestibular schwannoma?

Answer 29

Benign tumor that originates from schwann cells of the vestibular root (90% of cases and 5-10% of all intracranial tumors); typically found within cerebellopontine angle -> impinges on structures traversing internal acoustic meatus (VII, VIII, labyrinthine artery); slow growing

Question 30

What is vestibular neuritis? What are some treatments?

Answer 30

Thought to involve edema of the vestibular nerve/ganglion; patients present with severe vertigo, nausea, and vomiting, but no accompanying hearing loss or other CNS deficits Treatments: antiemetics, vestibular suppressants, corticosteroids, and antiviral agents

Question 31

Where do all vestibular nuclei project to?

Answer 31

Ventral posterior nuclear complex

Question 32

What do lesions in parietoinsular vestibular cortex cause?

Answer 32

Vertigo, unsteadiness, and loss of visual vertical

Question 33

What do lesions in posterior parietal cortex cause?

Answer 33

Confusion in spatial awareness

Question 34

What is the vestibuloocular reflex?

Answer 34

When turning your head, your eyes turn the opposite direction; at this moment, the eyes are at the back of the orbit and can't go back further; eyes intermittently and rapidly reset back to a central position

Question 35

What causes spontaneous nystagmus?

Answer 35

Silencing of output from damaged side = net differences in firing rates of CN VIII whe head is stationary; caused by unilateral damage to vestibular system; causes spontaneous nystagmus and may include vertigo, falls, and vomiting

Question 36

Describe peripheral damage as it relates to spontaneous nystagmus

Answer 36

Damage is to vestibular labyrinth and/or CN VIII; causes imbalance between left/right vestibular input and causes nystagmus; does not affect voluntary saccades and smooth pursuit

Question 37

Describe central damage as it relates to spontaneous nystagmus

Answer 37

Damage is to brainstem or cerebellar structures; causes nystagmus with impaired voluntary saccades and/or smooth pursuit; involvement of multiple pathways or cortical areas

Question 38

What is the caloric test?

Answer 38

Tests vestibular labyrinth function/VOR (vestibuloocular reflex) without moving the head; uses water to alter convection currents in endolymph that alters CN VIII firing rate

Question 39

What does warm water cause in the caloric test?

Answer 39

Generates currents that mimic turning head to irrigated side; nystagmus that beats toward irrigated ear

Question 40

What does cold water cause in the caloric test?

Answer 40

Opposite effect of warm water; nystagmus that beats away from irrigated ear

Question 41

What is the oculocephalic reflex/head thrust test?

Answer 41

Rotating the head back and forth horizontally that induces compensatory eye movements that are dependent on visual and vestibular function; reflex occurs when eyes move in opposite direction of the head movements -> doll's eyes

Question 42

What happens in conscious patients when testing the oculocephalic reflex? Comatose patients?

Answer 42

Conscious: doll's eyes are absent due to voluntary eye movements that mask the reflex Comatose: reflex is used to assess brainstem function; if the brainstem is intact the doll's eye reflex is present; if brainstem contains a lesion, doll's eye reflex is absent