Help from neuro masters- Vestibul-ocular reflexes

[Ramoray]

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I know this might be a pain but i am having the hardest time grasping this stuff and i thought i had it after reading about it in 3 sources but none seem to really give me the understanding. Then i looked at HY portion on it and that made no sense. SO if someone woudl be kidn enough, could anyone explain how the vestibulo ocular reflex works, mainly cinically in the caloric nystagmus tests and in general the concept. Also i dont understand HY vestibular v. postrotary terminology as it is not in any of my books. Yikes help please! thanks!

 

[Idiopathic]

This is what you need to know (as far as I am concerned).

When testing a patient using cold calorics, the mnemonic COWS is appropriate. This refers to Cold Opposite Warm Same.

When you turn your head to the left, your eyes track to the right (slow) and saccade to the left (fast) to keep up. This corresponds to a rotation of the right semicircular canal (picture the head rotating about either ear...that canal stays motionless). THUS, warming up of the right canal is analogous to rotation of the head around the left ear, with movement of the right canal.

Cold water poured in the right ear will make the head think that the other semicircular canal is active, and the eyes will have fast motion toward the opposite ear with nystagmus toward the affected ear.

Warm water in the right ear will have the opposite effect, making the head think that it is turning to the left, causing fast movement toward the affected ear.

Hence, COWS.

Keep in mind that the mnemonic COWS only applies to the fast tracking movements (smooth pursuit)

If this reflex is not intact, it is safe to assume that there is a lesion affecting the VOR, I believe. My knowledge in this is limited to what I learned in physiology, not in practice, however. This is most likely the type of question you would see on the boards, with the question perhaps testing whether you know the primary effector cell (hair cell), the ganglion involved (scarpa's), or any of the above.

Please correct any of this if it is wrong. It is all from memory.

 

[jakstat33]

Here's the knowledge I will take into the test with me (tmw):

the VOR keeps gaze stable while your head moves; vestibular nuclei -> MLF -> III, IV, VI. nystagmus- slow gaze-stabilization movement (VOR), then a fast reset movement in the opposite direction (depends on reticular formation); seen at the beg and end of rotation (opposite directions), or in response to caloric stimulation (as IDIO said, just remember COWS, cold = opp direction, warm = same direction). the Flocculus adjusts VOR if you want to turn it off or change its gain

the rest is history... 😱

 

[Ramoray]

thanks guys! man i tell you sadly i spent almost the entire day reading up and understanding this crap. I mean it was kind of interesting but its surprisingly hard to find a simple explanation in one source that covers everything. Nolte ended up being decent. it actually was the cdrappy pics in HY neuro that confused me. sometimes Hy is High yield because it slaps a few brief points instead of includding atleast some sorta explanation. I dont know but im getting sick of remembering this deviates this way when this happens or this side does this or the opposite side does this. Man so hard to keep track of when u think of everything you learn. but thanks guys that makes sense. much appreciated!

 

[jakstat33]

no prob, step 1 prep is all downhill once you get the VOR down 👍

thanks guys! man i tell you sadly i spent almost the entire day reading up and understanding this crap. I mean it was kind of interesting but its surprisingly hard to find a simple explanation in one source that covers everything. Nolte ended up being decent. it actually was the cdrappy pics in HY neuro that confused me. sometimes Hy is High yield because it slaps a few brief points instead of includding atleast some sorta explanation. I dont know but im getting sick of remembering this deviates this way when this happens or this side does this or the opposite side does this. Man so hard to keep track of when u think of everything you learn. but thanks guys that makes sense. much appreciated!