Vestibular

Question 1

the labyrinth (inner ear) is composed of…

Answer 1

1. cochlea
2. vestibule: utricle & saccule
3. semicircular canals

Question 1

what is the fluid of the bony labyrinth called and what is it continuous with?

Answer 1

perilymph (Na rich)
continuous with cerebrospinal fluid

Question 2

what is the fluid of the membranous labyrinth called?

Answer 2

endolymph (K rich)

Question 3

the membranous labyrinth communicates with the ____ which absorbs the continuously produced ____

Answer 3

endolymphatic sac
endolymph

Question 4

what is the purpose of the vestibular system?

Answer 4

helps with maintenance of posture, muscle tone, and eye position with respect to head motion

Question 5

the vestibular system is subdivided into the ____ and ____

Answer 5

static labyrinth
kinetic labyrinth

Question 6

the static labyrinth is composed of the ____ and the ____ which function to…

Answer 6

utricle + saccule
detect static orientation of the head with respect to gravity

Question 7

specialized hair cells in the static labyrinth are called ____ and ____

Answer 7

macula utricle
macula succuli

Question 8

the hair cells in the maculae are embedded in the ____ which contains ____

Answer 8

otolithic membrane (gelatinous mass)
CaCO3 crystals

Question 9

The kinetic labyrinth is composed of ____ which detect…

Answer 9

Semicircular canals
Angular acceleration and deceleration

Question 10

How are semicircular canals oriented and why?

Answer 10

Orthogonally
So they can detect all possible directions of motion

Question 11

Specialized hair cells in the semicircular canals are in the ____ and are called ____

Answer 11

Ampullae
Crista ampullaris

Question 12

Hair cells in the crista ampullaris are embedded in the ____

Answer 12

Cupula (gelatinous mass)

Question 13

transduction in the vestibular system occurs in the same way it does in the ____ system because…

Answer 13

auditory
endolymph is continuous between the 2 systems

Question 14

what ion flow causes hair cell depolarization in the vestibular system?

Answer 14

potassium influx

Question 15

when the microvilli bend toward the kinocilium, the cell will ____

Answer 15

depolarize

Question 16

when the microvilli bend away from the kinocilium, the cell will ____

Answer 16

hyperpolarize

Question 17

hair cell receptors synapse with dendrites of ____ whose axons form the ____ n

Answer 17

vestibular ganglia or Scarpa’s ganglia
vestibular n

Question 18

the vestibular nerve enters the brainstem at the ____ lateral to the ____

Answer 18

cerebellopontine angle
facial nerve

Question 19

where are vestibular nuclei located?

Answer 19

lateral aspect of floor of medullary and pontine part of 4th ventricle, underlying the vestibular area

Question 20

axons from the vestibular nuclei project to…

Answer 20

1. flocculonodular lobe & fastigal nucleus of cerebellum
2. spinal cord - vestibulospinal tract
3. brainstem nuclei of CN III, IV, & VI bilaterally via medial longitudinal fasciculus (MLF)
4. ventral posterior thalamic nucleus -> parietal association areas of cortex

Question 21

what is internuclear opthalmoplegia?

Answer 21

• failure of CNs III, IV & VI to carryout synchronous horizontal gaze due to lesion of MLF
• seen in MS or vascular disease
• not specific to vestibular disease

Question 22

how is the vestibular system examined?

Answer 22

Barany chair test
Caloric testing

Question 23

what is the Barany Chair test?

Answer 23

• rotate 10x in 20sec
• flex forward 30 degrees, rotation stops abruptly
• an intact system produces nystagmus opposite that of the rotation

Question 24

what is Caloric testing?

Answer 24

• warm or cold water in the external acoustic meatus
• cold water produces nystagmus to the opposite side of irrigation in an intact system
• warm water produces nystagmus to same side in an intact system

Question 25

symptoms of vestibular lesion

Answer 25

• vertigo
• nystagmus
• dysequillibrium

Question 26

central vestibular lesion may produce…

Answer 26

nystagmus in various directions in absence of vertigo during positional testing

Question 27

peripheral vestibular lesion may produce…

Answer 27

horizontal nystagmus only in the presence of vertigo

Question 28

Meniere’s Disease

Answer 28

• vestibular symptoms accompany progressive loss of hearing and tinnitus
• onset 20-30 years

Question 29

Acoustic Neuroma (Schwannoma)

Answer 29

• relatively common benign slow growing Schwann cell tumor of vestibular nerve
• typically found in IAM region or cerebellopontine angle
• may also affect CNs VII & V