Vestibular Ocular Reflex (M2) Flashcards
What is the test of vestibular function in which you produce a vestibular nystagmus using heat convection called? 1. What can this tell you? 2
- caloric stimulation
2. determine if canal is hyper or hypo
What is the disease of the vestibular system that is a change in the viscosity of the endolymph (hyper or hypo)?
Meniere’s disease
What is the timing of Benign paroxysmal positional vertigo? 1. Which canal is most commonly affected? 2
- sudden attack
2. posterior vertical
What is another term for linear acceleration? 1. What measured this? 2
- translational acceleration
2. otolith
If the left horizontal canal is constantly suppressed (hypo-stimulation) what would be the associated eye movements?
right beating nystagmus
What is the region of epithelium of both the utricle and saccule that contains a dense aggregate of hair cells that sense forces?
macula
What are the reasons for dizziness/oscillopsia when there is vestibular illness?
- mismatch between proprioception and VOR signals
2. mismatch between what you see and what your proprioception is telling you
When the head translates (linearly accelerates) what happens to the otolithic membrane?
membrane slides and pulls on cilia, causing an increase or decrease in firing rate
What happens to the phase and gain at lower frequencies of rotation (less than 0.01 cyc/sec)?
phase difference increases and gain falls
What type of movements does the saccule best respond to?
up and down translations of the head
What is the vertically oriented part of the otolith? 1. What does it respond to? 2
- saccule
2. vertical translational acceleration
What type of movements does the utricle best respond to?
- sustained lateral tilts (head to shoulder)
- sustained fore-aft tilts (pitch forward or backward)
- side to side translations of the head
What is the latency of translational VOR (TVOR)?
35ms
What is the antibiotic that can knock out the RVOR and leads to the person not being able to recognize faces or read street signs without standing still?
streptomycin
Does the likeliness of nystagmus increase or decreases if the head is moved in the orientation of the canal for Meniere’s disease?
increase
What are the plots that represent the relationship between gain and frequency along with phase and frequency?
Bode plot
What gives a response similar to the VOR but is initiated by stretch receptors in the neck rather than vestibular apparatus? 1. When is this important? 2
- cervico-ocular reflex
2. subjects who have lost normal vestibular function
What are the signs and symptoms of vestibular illness?
- vestibular nystagmus (worse when in direction of canal affected)
- dizziness/oscillopsia
- can’t see while walking
How are the kinocilium arranged in the otolith?
variable (different hair cells respond to forces in different directions)
What is test of VOR function that measures how the eye velocity (output) corresponds to the head velocity (input)? 1. How is it usually measured? 2. What is perfect score? 3
- gain (ratio of output velocity/input velocity)
- sinusoidal stimulation (rotate head back and forth)
- 1.00
What is caused by calcium carbonate crystals breaking free from the utricle and entering one of the canals? 1. What are the crystals called? 2
- Benign paroxysmal positional vertigo (BPPV)
2. otoconia
Where do the cilia of the macula in the utricle and saccule extend into? 1. What is contained there? 2
- otolithic membrane
2. crystals of calcium carbonate
Does vestibular neuritis cause hyper or hypo stimulation? 1. What are the possible causes of this? 2. Does the nystagmus increase or decrease when you turn your head in the direction of the affected canal? 3
- hypo
- viral infection, stroke, tumor, aneurysm, ischemia, MS
- increase or may increase in any direction if all canal affected
What is the common etiology of Benign paroxysmal positional vertigo for a person under age 50? 1. Over 50? 2
- head injury
2. idiopathic
What is a free floating otoconia called that leads to Benign paroxysmal positional vertigo? 1. An otoconia stuck to the cupula? 2
- canalithiasis
2. cupulothiasis
What is the horizontally oriented part of the otolith? 1. What does it respond to? 2
- utricle
2. horizontal translational acceleration and shift in gravity vector due to tilt
What is test of VOR function that measures the difference in position between eye and head? 1. What is a perfect score? 2
- phase
2. 180deg out of phase
What is the procedure for caloric stimulation?
- tilt head back 60deg so lateral canal vertical
- apply hot water (or cold to right ear) to the left ear
- induces leftward beating nystagmus (COWS= cold opposite, warm same)
What is the eye movement that refers to the cycloversion that accompanies tilt of the head? 1. What is the organ that is responsible for this? 2.
- counter-rolling
2. otolith organ
Does the likeliness of nystagmus increase or decreases if the head is moved in the orientation of the canal for Benign paroxysmal positional vertigo?
increase
If the left horizontal canal is constantly stimulated (hyper-stimulation) what would be the associated eye movements?
jerk nystagmus with left beating as fast phase left
In the otolith, does bending of the stereocilia towards the kinocilium cause depolarization or hyperpolarization? 1. Is this an increase or decrease in firing rate? 2
- depolarization
2. increase
